Frederick John MacIsaac (1882–1940), published as Fred MacIsaac, was an American pulp writer who contributed frequently to Argosy after World War I. His fiction ranged from crime and adventure to science fiction. The Mental Marvel follows a boxer with extraordinary mental powers, while The Vanishing Professor centers on an invisibility machine and the criminals and detectives drawn to it.

MacIsaac also wrote lost-world and future-disaster stories, including The Last Atlantide and The Hothouse World. His career is closely associated with Argosy and its companion titles, where his serial fiction reached a broad popular readership.