Japanese mycologist. Kobayasi was the second curator of the mycological herbarium at the National Science Museum, Tokyo (1946-1972). A botany graduate from the University of Tokyo, Kobayasi initially carried out research on flowering plants. His interest in fungi began while he was an undergraduate in the late 1920s, but he apparently did not collect any fungi during a 1931 visit to the Aleutian Islands. Following this trip he became an associate professor at Tokyo Bunrika Daigaku and published his first mycological paper in 1933, on Lasiophaera. He went on to become an expert on the genus Cordyceps and its allies, and described more than 15 new genera and 180 species.

Before joining the National Science Museum Kobayasi spent six years in China as a curator at the Central National Museum of Manchoukuo in Hsinking (Changchun). In the years following his return to Tokyo in 1946 he organised many expeditions, collecting fungi in the Pacific Islands and New Guinea, Antarctica, Greenland and Alaska.

Kobayasi was instrumental in the procurement of new premises in the Tsukuba suburb for the life sciences and geology departments of the National Science Museum. The museum's botany department thus moved to the site of the Tsukuba Botanical Gardens at the time of Kobayasi's retirement. Kobayasi continued his research after 1972, making more collecting trips to Africa and South America.

Sources:
E.J.H. Corner, 1993, "Dr. Yosio KOBAYASI 1907-1993", Transactions of the Mycological Society of Japan, 34(3): 295-297
Y. Doi, 2002, "Past and Present Conditions of the Mycological Herbarium in the National Science Museum, Tokyo (TNS)", National Science Museum Monographs, 22: 63-65.