Jan Mikusiński (April 3, 1913 – July 27, 1987) was a Polish mathematician based at the University of Wrocław known for his pioneering work in mathematical analysis.
Mikusiński was born in Stanisławów in 1913 and developed an operational calculus, known as the Calculus of Mikusiński (MSC 44A40), which is relevant for solving differential equations. His operational calculus is based upon an algebra of the convolution of functions with respect to the Fourier transform. From the convolution product he goes on to define what in other contexts is called the field of fractions or a quotient field. These ordered pairs of functions Mikusiński calls "operators", the "Mikusiński operators".
He is also well known for Mikusinski's cube, the Antosik–Mikusinski theorem, and Mikusinski convolution algebra.
Mikusiński died in Katowice in 1987. A street in Katowice is named after him.