William Willis FRCS (1 May 1837 – 14 February 1894) was an Irish medical doctor who joined the British mission in Japan in 1861.

[4] Among his students was Takaki Kanehiro, the first scientist-physician to prove that beriberi was connected to malnutrition, and the founder of Japan's first private medical college.

During the unsettled years at the end of the Tokugawa bakufu and the early Meiji Restoration, Willis treated the British nationals wounded in the Namamugi Incident and the Bombardment of Kagoshima.

Willis married a Japanese woman in Kagoshima, Enatsu Yae (1850-1931), the daughter of a former retainer of Shimazu Nariakira, with whom he had a son, Albert (1873-1943).

In 1885, Willis was appointed, on the recommendation of his good friend Ernest Satow, as a doctor with the British Consulate General in Bangkok.