Aldo Luigi Mario Castellani, Marchese di Chisimajo, KCMG (8 September 1874[1] – 3 October 1971) was an Italian pathologist and bacteriologist.

He demonstrated the cause and means of transmission of sleeping sickness, discovered the spirochete of yaws, and did other original work in bacteriology and in parasitic diseases of the skin.

In 1903 he was appointed Bacteriologist to the Government of Ceylon at the Central laboratory in Colombo and continued research in mycology and bacteriology, describing several new species of intestinal bacilli.

[3] He became lecturer on mycology and mycotic diseases at the London School of Hygiene and Tropical Medicine,[4] and established a consulting practice in Harley Street.

Castellani's enthusiasm for Royal and eminent patients such as Benito Mussolini clouded his reputation and during World War II he supported Italy against the Allies, becoming chief of the Italian Army's medical service.