Nuveen Municipal Opportunity Fund, Inc. (the Fund) is a closed-end investment company. The fund seeks current income exempt from regular federal income tax. The secondary investment objective is the enhancement of portfolio value. The fund invests in municipal securities that are exempt from federal income taxes. The fund invests at least 80% of its managed assets in municipal securities rated investment grade (Baa/BBB or better by S&P, Moody's, or Fitch) at the time of investment, or, if they are unrated, are judged by the manager to be of comparable quality. The fund may invest up to 20% of its managed assets in municipal securities rated below investment quality or judged by the manager to be of comparable quality, of which up to 10% of its managed assets may be rated below B-/B3 or of comparable quality. The fund uses leverage. The Fund's investment adviser is Nuveen Fund Advisors, Inc.