thumb|200px|Mitsuishi District in Hidaka Subprefecture before merging with Shizuani District in 2006.
was a district located in Hidaka Subprefecture, Hokkaido, Japan.
As of 2004, the district had an estimated population of 4,950 and a density of 14.30 persons per km<sup>2</sup>. The total area was 346.23 km<sup>2</sup>.
On March 31, 2006, Mitsuishi District merged with Shizunai District to create the new Hidaka District. Mitsuishi District and Shizunai District were both dissolved with this merger.
Towns and villages
- Mitsuishi