Masato Seto (瀬戸正人 Seto Masato?) is a Japanese–Thai photographer.
Seto was born in Udon Thani, Thailand, to a Japanese father and a Vietnamese Thai mother. He moved to Fukushima Prefecture, Japan in 1961, and studied photography at Tōkyō Shashin Senmon Gakkō (東京写真専門学校), graduating in 1973. After further study under Daidō Moriyama, Seto became an assistant to Masahisa Fukase in 1978. In 1981 he became a freelance.
Seto has worked on various photographic projects. The best known may be Living Room, an exhibition and then a book of a strip of single and group portraits of Japanese and foreign residents of Tokyo in their homes. This won the Kimura Ihei Award.
Seto in 2008 had his first solo show of photographs in his native country of Thailand. The exhibition featured his first two series of color photographs "Picnic" and "Binran." The show was put together by curator Connelly La Mar with support from the Japan Foundation in February  at H Gallery.
Yancey Richardson Gallery [www.yanceyrichardson.com] in New York City now represents his work for the U.S. market.
Books by Seto
- Bankoku, Hanoi 1982–1987 (バンコク、ハノイ 1982–1987). ICP, 1989. ISBN 4-87198-784-1. Photograph collection.
- Heya (部屋) / Living Room Tokyo. Tokyo: Shinchōsha, 1996. ISBN 4-10-413101-6. Photograph collection.
- Silent Mode. Tokyo: Mole, 1996. Photograph collection.
- Tooi to Masato (トオイと正人). Tokyo: Asahi Shinbunsha, 1998. ISBN 4-02-257265-5. New edition as Ajia kazoku monagatari (アジア家族物語). Tokyo: Kadokawa, 2002. ISBN 4-04-367601-8. Essay collection.
- Picnic. Place M, 2005. ISBN 4-901477-21-8.
- (Japanese) Hayashida (林田裕章). "Shashinka Seto Masato no jiden Tooi to Masato no butai (Udōntani–Tai)" (写真家・瀬戸正人氏の自伝「トオイと正人」の舞台（ウドーンタニ＝タイ）). Yomiuri Shinbun 9 May 2005. Yomiuri Online.
- Ono, Philbert. "Living Room, Tokyo — Heya". PhotoGuide Japan. A review of the book.
- (Japanese) Seto's site