The Hii River (斐伊川, Hii-kawa) is a river on the island of Honshu in Shimane Prefecture and Tottori Prefecture, Japan. With a length of 153 km and catchment of 2540 km2, it is the largest river in the east of Shimane Prefecture. It flows through the cities of Izumo and Matsue and through the lakes Shinji and Nakaumi and discharges into the Sea of Japan. In the antiquity the river was known as "Izumo-no-okawa" (出雲大川, "The great Izumo river").