Jakub Karol Parnas, also known as Yakov Oskarovich Parnas (Russian: ???? ????????? ??????) (January 16, 1884 – January 29, 1949) was a prominent Jewish-Polish–Soviet biochemist who contributed to the discovery of the Embden–Meyerhof–Parnas pathway, together with Otto Fritz Meyerhof and Gustav Georg Embden.
He became a Soviet activist after the annexation of Western Ukraine in 1939.
He was arrested during the Stalinist Jewish Anti-Fascist Committee affair in 1949 and died in the prison, reportedly of heart attack.