was a town located in Mitsuishi District, Hidaka Subprefecture, Hokkaido, Japan.
As of 2004, the town 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 was merged with the town of Shizunai (from Shizunai District) to create the new town of Shinhidaka (in the newly created Hidaka District).