| Kostyantyn Masyk | |
| Office: | Deputy chairman of Council of Ministers |
| Term Start: | 11 September 1981 |
| Term End: | 18 August 1986 |
| Primeminister: | Oleksandr Liashko |
| Term Start1: | July 1989 |
| Term End1: | 3 August 1990 |
| Primeminister1: | Vitaliy Masol |
| Office2: | First Vice Prime Minister (First deputy chairman) |
| Term Start2: | 3 August 1990[1] |
| Term End2: | October 1992 |
| Primeminister2: | Vitaliy Masol Vitold Fokin |
| Office3: | Prime Minister |
| Term Start3: | October 1990 |
| Term End3: | November 1990 |
| Predecessor3: | Vitaliy Masol |
| Successor3: | Vitold Fokin |
| Term Start4: | August 1991[2] |
| Term End4: | August 1991 |
| Predecessor4: | Vitold Fokin |
| Successor4: | Vitold Fokin |
| Office5: | Ambassador of Ukraine to Finland |
| Term Start5: | 1992 |
| Term End5: | June 1997 |
| President5: | Leonid Kravchuk Leonid Kuchma |
| Predecessor5: | post revived |
| Successor5: | Ihor Podolyev |
| Birth Date: | 9 July 1936 |
| Birth Place: | Volochysk, Vinnytsia Oblast, Ukrainian SSR, Soviet Union |
| Party: | Communist Party of Ukraine (1962–1991) |
| Occupation: | state official, diplomat |
| Signature: | Kostyantyn Masyk Signature 1990.png |
| Birth Name: | Kostyantyn Ivanovych Masyk |
| Native Name Lang: | uk |
Kostyantyn Ivanovych Masyk (Ukrainian: Костянтин Іванович Масик; 9 July 1936) is a Soviet and Ukrainian state official and diplomat.
Masyk was born in Volochysk. 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 1960s he became an activist of Komsomol of Ukraine becoming its first secretary in Kyiv and Kyiv Oblast.
In 1962 Masyk joined the Communist Party of the Soviet Union and finished the Higher Party School. In 1970s he served on the party's positions in Kyiv and Odesa. 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.
Later Masyk joined Party of Regions.