Kostyantyn Ivanovych Masyk (Ukrainian: Костянтин Іванович Масик; 9 July 1936) is a Soviet and Ukrainian state official and diplomat.

A graduate of the Gorky Institute of Water Transport Engineers, Masyk's working career started at the Kyiv factory of ship construction and repair in 1959–60.

In 1980s Masyk was a deputy chairman of council of ministers of the Ukrainian SSR and the First secretary of the Kyiv city party committee.

In 1990-1992 Masyk was a first deputy chairman and vice-prime Minister of Ukraine and was acting head of government soon after ousting of Vitaliy Masol following the 1990 Kyiv students' hunger strike.

In 1992–1997 he served as an ambassador of Ukraine to Finland and after that director of Nadra Bank.