Sosei (素性 or 素性法師, c. 816—910) was a Japanese waka poet and Buddhist priest. He is reckoned as one of the Thirty-six Poetry Immortals, and one of his poems was included in the famous anthology Hyakunin Isshu. His father Henjo was also a waka poet and monk.
Sosei entered religious life together with his father after the death of Emperor Nimmyō in 850.