Pioneer Municipal High Income Trust - Quarterly Schedule of Portfolio Holdings of Registered Management Investment Company (N-Q)

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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-Q

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-21321

Pioneer Municipal High Income Trust
(Exact name of registrant as specified in charter)

60 State Street, Boston, MA 02109
(Address of principal executive offices) (ZIP code)

Dorothy E. Bourassa, Pioneer Investment Management, Inc.,
60 State Street, Boston, MA 02109
(Name and address of agent for service)

Registrant's telephone number, including area code: [phone]

Date of fiscal year end: April 30

Date of reporting period: July 31, 2008

Form N-Q is to be used by management investment companies, other than small business investment companies registered on Form N-5 (239.24 and 274.5 of this chapter), to file reports with the Commission, not later than 60 days after close of the first and third fiscal quarters, pursuant to Rule 30b1-5under the Investment Company Act of 1940 (17 CFR 270.30b-5). The Commission may use the information provided on Form N-Q in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-Q, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-Q unless the Form displays a currently valid Office of Management and Budget ("OMB") control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609. The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. ss. 3507.

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ITEM 1. Schedule of Investments.

Pioneer Municipal High Income Trust
SCHEDULE OF INVESTMENTS 7/31/08 (unaudited)

Principal Amount ($) Value ($) TAX EXEMPT OBLIGATIONS - 129.0% of Net Assets Alabama - 1.3% 1,500,000 Camden Alabama Industrial Development Board, 6.125%, 1,462,860 1,000,000 Huntsville-Redstone Village Special Care Facilities F 847,610 2,000,000 Huntsville-Redstone Village Special Care Facilities F 1,583,660 3,894,130 Arizona - 2.1% 5,000,000 Apache County Industrial Development Authority, 5.85% 4,775,550 980,000 Pima County Industrial Development Authority, 7.25%, 1,004,304 500,000 Yavapai County Industrial Development Authority, 6.0% 496,800 6,276,654 California - 5.9% 5,150,000 + Golden State Tobacco Securitization Corp., 7.8%, 6/1/ 6,110,114 7,000,000 + Golden State Tobacco Securitization Corp., 7.875%, 6/ 8,327,130 2,500,000 University of California Revenue, 5.0%, 5/15/25 2,530,575 655,000 Valley Health System Hospital Revenue, 6.5%, 5/15/25 480,639 17,448,458 Connecticut - 5.1% 10,335,00(a) Lehman Municipal Trust Receipts, RIB, 8.573%, 7/1/42 10,636,369 5,000,000 Mohegan Tribe Indians Gaming Authority, 6.25%, 1/1/31 4,531,500 15,167,869 Delaware - 0.4% 765,000 Sussex County Delaware Revenue, 5.9%, 1/1/26 691,682 600,000 Sussex County Delaware Revenue, 6.0%, 1/1/35 524,928 1,216,610 District of Columbia - 3.6% 5,000,000 District of Columbia Tobacco Settlement Financing Cor 4,714,350 6,000,000 District of Columbia Tobacco Settlement Financing Cor 5,937,180 10,651,530 Florida - 6.4% 2,000,000 Beacon Lakes Community Development, 6.9%, 5/1/35 1,888,320 7,000,000(a) Lehman Municipal Trust Receipts, RIB, 8.16%, 11/1/39 7,190,470 2,500,000 Liberty County Subordinate Revenue, 8.25%, 7/1/28 2,461,375 1,000,000 St. Johns County Industrial Development Authority Rev 839,080 2,000,000 St. Johns County Industrial Development Authority Rev 1,550,880 5,000,000 Tallahassee Health Facilities Revenue, 6.375%, 12/1/3 5,033,250 18,963,375 Georgia - 6.6% 4,240,000(a) Atlanta Georgia Water & Waste Revenue, RIB, 8.049%, 1 3,967,877 2,400,000 Fulton County Residential Care Facilities Revenue, 5. 1,957,080 2,600,000 Fulton County Residential Care Facilities Revenue, 5. 1,980,342 7,500,000 Main Street Natural Gas Project Revenue, 6.25%, 7/15/ 6,775,350 4,500,000 Main Street Natural Gas Project Revenue, 6.375%, 7/15 4,102,290 1,000,000 Rockdale County Development Authority Revenue, 6.125% 954,780 19,737,719 Guam - 1.5% 5,000,000 Northern Mariana Islands, 5.0%, 10/1/22 4,370,800 Idaho - 1.6% 5,000,000 Power County Industrial Development Corp., 6.45%, 8/1 4,904,400 Illinois - 5.6% 1,000,000 Centerpoint Intermodal Center, 8.0%, 6/15/23 (144A) 913,550 1,000,000 Illinois Finance Authority Revenue, 6.0%, 11/15/27 910,630 1,000,000 Illinois Finance Authority Revenue, 6.0%, 11/15/39 871,350 1,500,000 Illinois Health Facilities Authority Revenue, 6.9%, 1 1,137,150 16,880,00(b) Metropolitan Pier & Exposition Authority Dedicated St 11,387,923 1,800,000 Southwestern Illinois Development Authority Revenue, 1,584,828 16,805,431 Indiana - 3.3% 5,000,000 Indiana Health & Educational Facility Financing Autho 4,437,050 1,000,000 Indiana State Development Finance Authority Revenue, 939,340 4,300,000 Indiana State Development Finance Authority Revenue, 4,332,981 9,709,371 Louisiana - 2.0% 1,500,000 Louisiana Local Government Environmental Facilities R 1,456,140 5,000,000 Louisiana Public Facilities Authority Revenue, 5.5%, 4,665,250 6,121,390 Massachusetts - 6.1% 7,050,000 Massachusetts Health & Educational Facilities Authori 7,152,295 3,500,000 Massachusetts Health & Educational Facilities Authori 3,520,300 2,500,000 Massachusetts Health & Education Facilities Authority 2,362,625 5,000,000 Massachusetts Health & Educational Facilities Authori 4,990,350 18,025,570 Michigan - 3.2% 950,000 Doctor Charles Drew Academy, 5.7%, 11/1/36 639,084 1,700,000 Flint Michigan Hospital Building Authority Revenue, 5 1,586,457 1,500,000 John Tolfree Health System Corp., 6.0%, 9/15/23 1,445,085 2,000,000 Michigan State Hospital Finance Authority Revenue, 5. 1,806,260 4,010,000 Michigan State Hospital Finance Authority Revenue, 6. 4,010,000 9,486,886 Minnesota - 2.3% 1,675,000 Duluth Economic Development Authority Health Care Fac 1,739,069 1,500,000 North Oaks Senior Housing Revenue, 6.0%, 10/1/33 1,384,905 2,000,000 North Oaks Senior Housing Revenue, 6.125%, 10/1/39 1,856,760 2,000,000 North Oaks Senior Housing Revenue, 6.5%, 10/1/47 1,955,400 6,936,134 Mississippi - 1.0% 3,000,000 Mississippi Business Finance Corp. Pollution Control 2,885,040 Montana - 0.4% 1,600,000 Two Rivers Authority, Inc. Correctional Facility Impr 1,146,592 Nebraska - 0.7% 2,000,000 Grand Island Solid Waste Disposal Facilities Revenue, 1,988,800 Nevada - 1.5% 4,600,000 Clark County Industrial Development Revenue, 5.5%, 10 3,915,198 2,000,000 Nevada State Department of Business & Industry, 7.25% 575,760 4,490,958 New Jersey - 9.5% 2,000,000 New Jersey Economic Development Authority Revenue, 6. 1,575,460 13,350,000 New Jersey Economic Development Authority Revenue, 6. 9,564,340 1,000,000 New Jersey Economic Development Authority Revenue, 6. 763,580 6,150,000 New Jersey Economic Development Authority Revenue, 7. 4,804,749 10,000,00 + Tobacco Settlement Financing Corp., 6.75%, 6/1/39 11,619,800 28,327,929 New Mexico - 1.4% 1,500,000 Otero County New Mexico Project Revenue, 6.0%, 4/1/23 1,389,540 2,960,000 Otero County New Mexico Project Revenue, 6.0%, 4/1/28 2,628,776 4,018,316 New York - 9.5% 2,500,000 Albany New York Industrial Development Agency Civic F 2,380,400 2,000,000 Nassau County New York Industrial Development Agency 1,972,860 2,000,000 New York City Industrial Development Agency, 5.375%, 1,837,640 12,990,000 New York City Industrial Development Agency, 6.9%, 8/ 5,849,657 7,040,000(a) New York State Dormitory Authority Revenue, RIB, 9.97 7,920,986 2,000,000 Suffolk County Industrial Development Agency, 7.25%, 2,035,660 6,000,000 Triborough Bridge & Tunnel Authority Revenue, 5.25%, 6,115,920 28,113,123 North Carolina - 2.2% 4,030,000 Charlotte North Carolina Special Facilities Revenue, 2,697,642 4,600,000 Charlotte North Carolina Special Facilities Revenue, 3,952,596 6,650,238 Oklahoma - 7.0% 3,000,000 + Oklahoma Development Finance Authority Revenue, 5.625 3,139,260 8,000,000 + Oklahoma Development Finance Authority Revenue, 5.625 8,371,360 4,100,000 Tulsa Municipal Airport Revenue, 5.65%, 12/1/35 4,051,005 1,225,000 Tulsa Municipal Airport Revenue, 6.25%, 6/1/20 965,276 4,350,000 Tulsa Municipal Airport Revenue, 7.35%, 12/1/11 4,119,059 20,645,960 Pennsylvania - 7.3% 3,000,000 Allegheny County Hospital Development Authority Reven 2,382,180 1,550,000 Allegheny County Hospital Development Authority Reven 1,459,278 12,300,00 + Allegheny County Hospital Development Authority Reven 14,361,357 1,000,000 Columbia County Hospital Authority Health Care Revenu 832,560 925,000 Hazleton Health Services Authority Hospital Revenue, 870,221 1,280,000 Langhorne Manor Borough Higher Education & Health Aut 1,233,587 500,000 Pennsylvania Higher Educational Facilities Authority 477,795 21,616,978 Rhode Island - 1.3% 4,000,000 Central Falls Detention Facilities Revenue, 7.25%, 7/ 4,009,600 South Carolina - 2.3% 5,185,000 + South Carolina Jobs Economic Development Authority Re 5,926,196 665,000 + South Carolina Jobs Economic Development Authority Re 757,428 6,683,624 Tennessee - 3.7% 7,000,000 + Johnson City Health & Educational Facilities Board Ho 8,296,400 2,480,000 Knox County Health Educational & Housing Facilities B 2,579,051 10,875,451 Texas - 14.6% 1,345,000 Bexar County Housing Finance Corp., 8.0%, 12/1/36 1,335,814 1,000,000 Dallas-Fort Worth International Airport Revenue, 6.0% 510,460 4,000,000 Decatur Hospital Authority Revenue, 7.0%, 9/1/25 4,023,200 1,000,000 + Georgetown Health Facilities Development Corp., 6.25% 1,057,990 2,000,000 Gulf Coast Industrial Development Authority Revenue, 1,746,240 3,750,000 Houston Airport System Special Facilities Revenue, 5. 2,459,400 5,340,000 Lubbock Health Facilities Development Corp., 6.625%, 5,087,258 10,000,000 North Texas Tollway Authority Revenue, 5.75%, 1/1/33 9,718,500 2,450,000(a) Northside Independent School District, RIB, 9.169%, 6 2,491,944 500,000 Sabine River Authority Pollution Control Revenue, 6.1 402,770 7,040,000(a) Texas State, RIB, 9.134%, 4/1/30 (144A) 7,305,830 735,000 (c) Willacy County Local Government Corp. Revenue, 6.0%, 751,420 1,500,000 Willacy County Local Government Corp. Revenue, 6.0%, 1,484,160 5,250,000 Willacy County Local Government Corp. Revenue, 6.875% 4,948,493 43,323,479 Utah - 0.2% 800,000 Spanish Fork City Charter School Revenue, 5.55%, 11/1 703,128 Vermont - 0.5% 1,500,000 Vermont Educational & Health Buildings Financing Agen 1,549,740 Virginia - 0.3% 1,000,000 Peninsula Ports Authority, 6.0%, 4/1/33 938,850 Washington - 7.9% 4,710,000 Spokane Public Facilities District Hotel/Motel Tax & 5,023,121 7,025,000 Tobacco Settlement Authority Revenue, 6.625%, 6/1/32 6,871,995 14,315,000 Washington State General Obligation, 0.0%, 6/1/22 7,065,455 5,000,000 Washington State Housing Finance Committee Nonprofit 4,529,850 23,490,421 Wisconsin - 0.7% 2,400,000 Aztalan Wisconsin Exempt Facilities Revenue, 7.5%, 5/ 2,005,752 TOTAL TAX-EXEMPT OBLIGATIONS (Cost $385,918,633) 383,180,306

MUNICIPAL COLLATERALIZED DEBT OBLIGATION - 3.3% of Net Assets

10,000,00(d)(Non-Profit Preferred Funding Trust I,12.0%, 9/15/37 ( 9,654,600
TOTAL MUNICIPAL COLLATERALIZED DEBT OBLIGATION

(Cost $10,000,000) 9,654,600 Shares COMMON STOCK - 0.6% of Net Assets 194,770 (f) Northwest Airlines Corp. 1,784,093 TOTAL COMMON STOCK (Cost $6,612,756) 1,784,093 TOTAL INVESTMENTS IN SECURITIES - 132.9% (Cost $402,531,389) (g)(h) 394,618,999 OTHER ASSETS AND LIABILITIES - 1.1% 3,407,266 PREFERRED SHARES AT REDEMPTION VALUE, INCLUDING DIVIDENDS PAYABLE - (34.0)% (101,014,388) NET ASSETS APPLICABLE TO COMMON SHAREOWNERS - 100.0% 297,011,877 RIB Residual Interest Bonds NR Security not rated by S&P or Moody's. (144A) Security is exempt from registration under Rule 144A of the Securities Act of 1933. Such securities may be resold normally to qualified institutional buyers in a transaction exempt from registration. At July 31, 2008 the value of these securities amounted to $50,784,754 or 17.1% of net assets applicable to common shareowners. + Prerefunded bonds have been collateralized by U.S. Treasury securities or U.S. Government Agencies which

are held in escrow to pay interest and principal on the tax exempt issue and to retire the bonds in full at the earliest refunding date.

(a) The interest rate is subject to change periodically and inversely based upon prevailing market rates. The interest rate shown is the coupon rate at July 31, 2008.

(b) Debt obligation initially issued at one coupon which converts to a higher coupon at a specific date. The rate shown is the coupon rate at July 31, 2008.

(c) Escrow to maturity.

(d) The interest rate is subject to change periodically. The interest rate shown is the coupon rate at July 31, 2008.

(e) Indicates a security that has been deemed illiquid. The aggregate cost of illiquid securities is $10,000,000. The aggregate value $9,654,600 represents 3.3% of the net assets.

(f) Non-income producing.

(g) The concentration of investments by type of obligation/ market sector is as follows:
Insured:

MBIA

5.7% FGIC 1.8 FSA 1.0 ACA 0.9 AMBAC 0.7 General Obligation 7.3 Revenue Bonds: Health Revenue 27.0 Tobacco Revenue 11.1 Airport Revenue 10.3 Other Revenue 6.1 Development Revenue 5.2 Facilities Revenue 4.7 Education Revenue 4.5 Pollution Control Revenue 3.5 Utilities Revenue 2.8 Housing Revenue 2.8 Transportation Revenue 2.6 Gaming Revenue 1.2 School District Revenue 0.6 Power Revenue 0.2

100.0%

(h) At July 31, 2008, the net unrealized loss on investments based on cost for federal income tax purposes of $400,665,447 was as follows:

Aggregate gross unrealized gain for all investments i $ 2
there is an excess of value over tax cost

Aggregate gross unrealized loss for all investments i (2
there is an excess of tax cost over value $ (
Net unrealized loss

For financial reporting purposes net unrealized loss on investments was $(7,912,390) and cost of investments aggregated $402,531,389

ITEM 2. CONTROLS AND PROCEDURES.

(a) Disclose the conclusions of the registrant's principal executive officer or officers and principal financial officer or officers, or persons performing similar functions, about the effectiveness of the registrant's disclosure controls and procedures (as defined in Rule 30a-3(c) under the Act (17 CFR 270.30a-3(c))) as of a date within 90 days of the filing date of the report that includes the disclosure required by this paragraph, based on their evaluation of these controls and procedures required by Rule 30a-3(b) under the Act (17 CFR270.30a-3(b))) and Rule 13a-15(b) or 15d-15(b) under the Exchange Act (17 CFR240.13a-15(b) or 240.15d-15(b)).

The registrant's principal executive officer and principal financial officer have concluded that the registrant's disclosure controls and procedures are effective based on their evaluation of these controls and procedures as of a date within 90 days of the filing date of this report.

(b) Disclose any change in the registrant's internal controls over financial reporting (as defined in Rule 30a-3(d) under the Act (17 CFR270.30a-3(d)) that occurred during the registrant's last fiscal quarter that has materially affected, or is reasonably likely to materially affect, the registrant's internal control over financial reporting.

There were no significant changes in the registrant's internal control over financial reporting that occurred during the second fiscal quarter of the period covered by this report that have materially affected, or are reasonably likely to materially affect, the registrant's internal control over financial reporting.

ITEM 3. EXHIBITS.

(a) A separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule 30a-2 under the Act (17 CFR 270.30a-2).

Filed herewith.

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SIGNATURES

[See General Instruction F]

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant) Pioneer Municipal High Income Trust

By (Signature and Title)* /s/ John F. Cogan, Jr. John F. Cogan, Jr, President Date September 29, 2008

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)* /s/ John F. Cogan, Jr. John F. Cogan, Jr., President Date September 29, 2008 By (Signature and Title)* /s/ Mark Bradley Mark Bradley, Treasurer Date September 29, 2008

* Print the name and title of each signing officer under his or her signature.