The Diocese of Oita (Latin: Dioecesis Oitaensis, Japanese: カトリック大分教区, romanized: Katorikku Ōita Kyōku) is a suffragan Latin Church diocese of the Catholic Church in the ecclesiastical province of the metropolitan Nagasaki in southern Japan.

Its cathedral episcopal see is the Cathedral of St. Francis Xavier (Oita Church), in the city of Ōita.

The first Catholic jurisdiction of Otai's territory was established on 19 February 1588, during Portuguese colonial prominence and missionary efforts in the Far East, as the Diocese of Funai (or Funay), on territory split off from the colonial Roman Catholic Diocese of Macau.

It was suppressed around 1660, having had the following incumbents (all Portuguese missionary members of Latin Congregations):

This article on a Roman Catholic diocese in Asia is a stub.