Nishiiwai (西磐井郡, Nishiiwai-gun) is a district located in Iwate Prefecture, Japan.
As of June 1, 2019, the district has an estimated population of 7,440 with a density of 117 inhabitants per square kilometre (300/sq mi). The total area is 63.39 km2 (24.48 sq mi).
After the third city of Ichinoseki creation on September 20, 2005, the district has only one town left.