Koiwai Station (小岩井駅, Koiwai-eki) is an East Japan Railway Company (JR East) railway station located in the city of Takizawa, Iwate Prefecture, Japan.

Koiwai Station is served by the Tazawako Line, and is located 10.5 km from the terminus of the line at Morioka Station.

Koiwai Station has a two opposed side platforms, connected to the wooden station building by a footbridge.

Koiwai Station opened on June 25, 1921.

The station was absorbed into the JR East network upon the privatization of the JNR on April 1, 1987.