Sylvester Kossów, Kosiv or Kosov (secular name Stefan-Adam Kosaw, Polish: Sylwester Kossów; born Zharobychi, Vitebsk Voivodeship, Polish–Lithuanian Commonwealth, died 13 April 1657) was the Metropolitan of Kiev, Galicia and all Rus'[a] in the Ecumenical Patriarchate of Constantinople in the Eastern Orthodox Church from 1647 to 1657.

With the opening of the Kyiv Lavra School in 1631, Kosiv be its lecturer on the request of Metropolitan Petro Mohyla becoming its prefect.

Despite being critical of some of the policies of the Ukrainian Cossacks, he attempted to rectify the situation and along with the Patriarch of Jerusalem Paiseus gave Bohdan Khmelnytsky a hero's welcome when he entered Kyiv on 2 January 1649 (Old Style 23 December 1648).

Kossów strived for an independent Ruthenian Orthodox Church that would be only under the jurisdiction of the Patriarch of Constantinople, and he fought against the subjugation of the Kyiv metropolate to Moscow.

In 1650 Sylvestr headed a delegation of the Orthodox clergy and Kyiv voivode Adam Kysil to the Sejm in Warsaw and contribute to ratification of the 1649 treaty of Zboriv.