Baron Matsumoto Jun (松本 順) (born Sato Junnosuke (佐藤 順之助); July 13, 1832 – March 12, 1907), previously known as Matsumoto Ryōjun (松本 良順), was a Japanese physician and photographer who served as the personal physician to the last shōgun, Tokugawa Yoshinobu.

He was sent to Nagasaki in 1857 to study rangaku, during which time he studied both western medicine and photography under the Dutch physician J. L. C. Pompe van Meerdervoort, though he was somewhat unimpressed with his instructor's skills, once describing the result of one of Pompe van Meerdervoort's photographic experiments as "a meagre black shadow".

Briefly imprisoned after the war by the new Meiji government, he was released through the efforts of Yamagata Aritomo, who asked him to help develop the medical corps of the fledgling Imperial Japanese Army.

He was also instrumental in helping Sugimura Yoshie (formerly Nagakura Shinpachi) and Fujita Gorō (formerly Saitō Hajime) build a monument Grave of Shisengumi at Itabashi in Tokyo in 1875.

He retired from the Imperial Army on April 1, 1902, and on March 2, 1905, he received the title of baron (danshaku) under the Kazoku peerage system.