Suwa Kofun - Tsukidate Castle ruins Ōsato (大郷町, Ōsato-chō) is a town located in Miyagi Prefecture, Japan.

The area of present-day Ōsato was part of ancient Mutsu Province, and has been settled since at least the Jōmon period by the Emishi people and a number of shell middens from that era have been found.

The area was organized into Ōya, Ōmatsuzawa and Kasukawa villages within Kurokawa District, Miyagi Prefecture with the establishment of the modern municipalities system on April 1, 1884.

Ōsato, together with the rest of Kurokawa District and the city of Tomiya collectively contributes two seats to the Miyagi Prefectural legislature.

In terms of national politics, the town is part of Miyagi 5th district of the lower house of the Diet of Japan.