Mary Stuart MacDougall (7 November 1885—1972) was an American biologist who studied protozoology.

[1] In 1920, MacDougall would become the head of the biology department at Agnes Scott College.

[2] Every summer, for fourteen years, MacDougall was an instructor and researcher at the Marine Biological Laboratory.

[1] She studied the polyploid and diploid of Chilodonella uncinata, as well as mutation inheritances found in them.

MacDougall also researched the chromosomes of plasmodium, avian malaria and neuromotors of chlamydodon.