San'yō (山陽町 San'yō-cho) is a town located in Asa District, Yamaguchi, Japan.
As of 2003, the town has an estimated population of 22,131 and a density of 246.42 persons per km². The total area is 89.81 km².
On March 22, 2005 San'yō was merged with the city of Onoda to form the new city of San'yō-Onoda.