Jan Ritzema Bos (25 July 1850, in Groningen – 7 April 1928, in Wageningen) was a Dutch plant pathologist and zoologist.

He served as the first director of the Willie Commelin Scholten Foundation and founder of the Plant Protection Service in 1899 in Amsterdam.

His brother was Hemmo Bos, author and lecturer at the agricultural college in Wageningen.

He went to study zoology at the University of Groningen in 1868 and received a doctorate with work under H.C. van Hall and M. Salverda in 1874.

The school closed down in 1871 and Bos moved to Warffum where he began to study plant diseases.