Suo (周防国 Suō no kuni) was a province of Japan in the area that is today the eastern part of Yamaguchi Prefecture. Suo bordered on Aki, Iwami, and Nagato Provinces.

The ancient provincial capital was in Hofu. Suo was ruled for much of the Muromachi period by the Ouchi clan, who built a castle at Yamaguchi, but in the Sengoku period it was conquered by the Mori clan, and was ruled remotely by them for much of the Edo period.