Oliver Erichson Janson (1850 – 25 November 1925) was an English entomologist who specialised in beetles.
Janson's early years were spent at Fortis Green, and he collected beetles there and at Finchley, Hampstead and Highgate.
During World War I, he made three trips to Ireland, particularly County Kerry.
Janson was a world authority on Cetoniinae publishing new genera and species mostly in Cistula Entomologica published by Janson and Co. His world collection was purchased by Titus Valck Lucassen.
His collection, in turn, was acquired by the Rijksmuseum van Natuurlijke Historie at Leiden in 1940.