Out of the 10 individuals in the Hollywood 10, 6 were Jewish.
Sources:
"Why The Hollywood Blacklist Is A Jewish Story (And Also A Milwaukee Story)" – The Jewish Daily Forward
"On this day: the Hollywood Ten are blacklisted" – The Jewish Chronicle
"Why The Hollywood Blacklist Is A Jewish Story (And Also A Milwaukee Story)" – The Jewish Daily Forward
"On this day: the Hollywood Ten are blacklisted" – The Jewish Chronicle