Nishiiwai (西磐井郡 Nishiiwai-gun?) is a district located in Iwate Prefecture, Japan.
As of 2005, the district has an estimated population of 8782. The total area is 63.39 km².
After the 3rd city of Ichinoseki creation on September 20, 2005, the district has only one town left.
Coordinates: 38°59′25″N 141°05′37″E / 38.990248°N 141.093708°E