The San'yō Region (山陽地方 San'yō-chihō) is an area in the south of Honshū, the main island of Japan. It consists of the southern part of the Chūgoku region, facing the Seto Inland Sea. The name San'yō means "southern, sunny (yō) side of the mountains" and contrasts with the San'in or "northern, shady (in) side of the mountains".
The region is generally considered to include the prefectures of Okayama, Hiroshima and Yamaguchi. Sometimes, the section of Hyōgo Prefecture that formerly comprised Harima Province is considered to be within the region as well.
The San'yō encompasses the pre-Meiji provincial areas of Harima, Mimasaka, Bizen, Bitchu, Bingo, Aki, Suō and Nagato.