| Kostiantyn Sytnyk | |
| Order: | Chairman of the Supreme Soviet of the Ukrainian SSR |
| Term Start: | 1980 |
| Term End: | 1985 |
| Predecessor: | Mykhailo Bilyi |
| Successor: | Platon Kostiuk |
| Order1: | Director of the Botanic Institute (NANU) |
| Term Start1: | 1970 |
| Term End1: | 2003 |
| Predecessor1: | Alfred Oksner |
| Successor1: | Yakiv Didukh |
| Birth Name: | Kostiantyn Merkuriyovych Sytnyk |
| Birth Date: | 3 June 1926 |
| Birth Place: | Luhanske, Luhansk Okruha, Ukrainian SSR, USSR |
| Death Place: | Kyiv, Ukraine |
| Party: | Ukrainian Platform "Sobor" |
| Otherparty: | All-Union Communist Party (bolsheviks) (1982–90) People's Democratic Party (1996–99) |
Kostiantyn Merkuriyovych Sytnyk (Ukrainian: Костянтин Меркурійович Ситник; 3 June 1926 – 22 July 2017) was a Ukrainian and Soviet scientist and academician, a member of the National Academy of Sciences of Ukraine who in 1970-2003 was director of the Botanic Institute of the National Academy of Sciences of Ukraine. Sytnyk also worked as a politician, and served as the Chairman of the Verkhovna Rada of the Ukrainian Soviet Socialist Republic from 1980 to 1985.
Sytnyk was born in Luhansk.