Johannes Theodorus Oudemans (1862-1934) was a Dutch entomologist and dendrologist. He worked as a lecturer in zoology at the University of Amsterdam and later became an estate manager.
He became the first chairman of the Vereniging Natuurmonumenten in 1905. In addition, he was a board member of the Dutch Zoo Society and the Dutch Entomological Society.
He was son of the botanist Cornelis Antonie Jan Abraham Oudemans and married to Jeanne Mathilde Christine Schober (1854-1940). From 1901 Oudemans managed the estate Schovenhorst near Putten, where the old Dutch pinetum can be found. The estate was owned by his father-in-law Schober.