Usa (宇佐郡 Usa-gun) was a district located in Ōita, Japan.
As of 2003, the district had an estimated population of 12,739 and the density of 48.85 persons per km². The total area was 260.79 km².
The district dissolved on March 31, 2005 when the district merged with the old city of Usa to form the new city of Usa.
Until March 30, 2005, the district had two towns.