Sado (佐渡国 Sado-no-kuni) was a province of Japan until the late 19th century; since then, it has been a part of Niigata Prefecture. It lies on the eponymous Sado Island, off the coast of Niigata prefecture (or in the past, Echigo province).

Sado was one of Japan's more remote areas, and nobles and aristocrats were often exiled to Sado when out of favor. People were also sent to mine silver and gold there. In the Kamakura period, the province was granted to the Honma clan from Honshu, and they continued to dominate Sado until 1589, when Uesugi Kagekatsu of Echigo Province took over the island. The Tokugawa shoguns later made Sado a personal fief after Sekigahara.

Today the entire island comprises Sado City, and the name Sado Province is obsolete.