was a town located in Hayami District, Ōita Prefecture, Japan.
As of 2003, the town had an estimated population of 8,590 and the density of 59.77 persons per km<sup>2</sup>. The total area was 143.71 km<sup>2</sup>.
On October 1, 2005, Yamaga, along with the village of Ōta (from Nishikunisaki District), was merged into the expanded city of Kitsuki.