Koshiji (越路町; -machi) was a town located in Santō District, Niigata, Japan.
As of 2003, the town had an estimated population of 14,160 and a density of 242.30 persons per km². The total area was 58.44 km².
On April 1, 2005 Koshiji, along with the town of Oguni, from Kariwa District, the village of Yamakoshi, from Koshi District, the town of Nakanoshima, from Minamikanbara District, and the town of Mishima, from Santō District, was absorbed into the city of Nagaoka.