Tessei (哲西町 Tessei-chō) was a town located in Atetsu District, Okayama, Japan.
On March 31, 2005 Tessei, along with the towns of Ōsa, Shingō and Tetta, all from Atetsu District, was merged into the expanded city of Niimi.
As of 2003, the town had an estimated population of 3,152 and a density of 41.32 persons per km ². The total area was 76.29 km ².
The town is known for its nature reserve.