Pioneer Municipal High Income Fund, Inc. is a closed-ended fixed income mutual fund launched and managed by Pioneer Investment Management, Inc. It invests in the fixed income markets of the United States. The fund primarily invests in municipal securities. It seeks to invest in securities across the credit rating and maturity spectrum. The fund benchmarks the performance of its portfolio against the Barclays Municipal Bond Index and Barclays High Yield Municipal Bond Index. Pioneer Municipal High Income Fund, Inc. was formed on March 13, 2003 and is domiciled in the United States.