Zenon Kossak (April 1, 1907 - 1939) was an activist in the Ukrainian militant nationalist movement for independence from interwar Poland.
Kossak was born in Drohobych in Galicia (then of the Austro-Hungarian Empire, now in Ukraine). He studied law at Lviv University and was one of the organizers of the nationalist movement in Galicia.
He was a member of the Ukrainian Military Organization in the late 1920s where he directed the 'combat', then the organizational, activities of the Organization of Ukrainian Nationalists in 1939 as a member of its Home Executive. He became deputy commander of the Carpathian Sich National Defense Organization in Carpatho-Ukraine. He was killed in action by Hungarian troops in Solotvyna, near Bukshtyn, in Transcarpathia.