Oshima is an island in Yamaguchi prefecture in Japan. Ooshima is connected with Honshu by a bridge. It is one of the largest islands in the Setonaikai strait. The area is about 130 square meters. There are 230,000 people on the island. The whole island is set aside as a national park. The special product is a mandarin orange called "Ooshima mikan". There are several orange groves.

There are beaches, campsites, fishing places and a hang gliding soit. Despite these things, population in the island is decreasing year after year.

The Ooshima Bridge was erected in 1976. The tide is known as one of the fastest in Japan. It is the second longest span in Japan of this style of bridge. The span of the bridge is 1020m. Its color is pale green.

Katazoegahama beach is one of the more popular beaches in the west of Japan. This is also famous for camping. There is a tennis court and a roller skate rink, near the beach. Furthermore, there is a resort hotel.

Ooshima is a sister city of Hawaii. There is a Hawaii historical museum, which was built in 1999 in Oshima. Office workers and bus drivers in town wear colorful aloha shirts as a uniform in summer.