William Purdom (10 April 1880 ??7 November 1921) was a British plant explorer sent by Veitch and the Arnold Arboretum of Harvard University to the northern provinces of China in 1909. He collected and photographed plants for the Arboretum along China??? Yellow River for three years, 1909??911.

In 1914 Purdom and a companion Reginald Farrer set out on an ambitious expedition to Tibet and the Province of Kansu province of North-west China. These two years of exploring and plant collecting are described in Farrer's 'On the Eaves of the World' (2 vols) (1917), and Farrer's posthumous 'The Rainbow Bridge (1921).