Ky Fan (樊𰋀, pinyin: Fán Qí, September 19, 1914 – March 22, 2010) was a Chinese-born American mathematician.

His father, named Fan Qi (樊琦, 1879—1947), served in the district courts of Jinhua and Wenzhou.

Initially Fan wanted to study engineering, but eventually shifted to mathematics, largely because of the influence of his uncle Feng Zuxun (冯祖荀, 1880–1940; b. Hangzhou, d. Beijing), who was a mathematician in China and the then Chair of the Department of Mathematics of Peking University.

That was an important reason for him to choose mathematics, with less English but full of equations, and go to Paris.

Fan was a student and collaborator of M. Fréchet and was also influenced by John von Neumann and Hermann Weyl.

The author of approximately 130 papers, Fan made fundamental contributions to operator and matrix theory, convex analysis and inequalities, linear and nonlinear programming, topology and fixed point theory, and topological groups.