was a village located in Koshi District, Niigata Prefecture, Japan.
As of 2003, the village had an estimated population of 2,035 and a density of 51.09 persons per km<sup>2</sup>. The total area was 39.83 km<sup>2</sup>.
On April 1, 2005, Yamakoshi, along with the town of Oguni (from Kariwa District), the town of Nakanoshima (from Minamikanbara District), and the towns of Koshiji and Mishima (both from Santà  District), was merged into the expanded city of Nagaoka.
On October 23, 2004, Yamakoshi was hit by the 2004 Chà «etsu earthquake.