Iossif Vladimirovich Ostrovskii (Ukrainian: Йосип Володимирович Островський, Russian: Иосиф Владимирович Островский, 6 April 1934 – 29 November 2020, in Ankara) was a Soviet and Ukrainian mathematician who made significant contributions to function theory and probability theory, Corresponding Member of the National Academy of Sciences of Ukraine (1978).

He obtained a degree at National University of Kharkiv in 1956, and entered post-graduate studies, where his supervisor was Boris Yakovlevich Levin.

In 1959 he defended his PhD thesis The connection between the growth of a meromorphic function and the distribution of its values by arguments.

In 1965 he defended his doctoral thesis Asymptotic properties of entire and meromorphic functions and some of their applications.

From 1986 to 2001 he headed the Department of Function Theory at Verkin Institute for Low Temperature Physics and Engineering.