Judah ben Tabbai was a Jewish religious leader of the early 1st century BCE. He was a contemporary of Simeon ben Shetach. During the persecution of the Pharisees under Alexander Jannaeus (r. 103-76 BCE), Judah fled to Alexandria, returning after Jannaeus' death. Judah b. Tabbai was accused by Simeon b. Shetach of wrongfully executing a witness for political purposes (namely, to send a message to the opposition Sadducee party). Judah b. Tabbai then resolved to judge only according to Simeon b. Shetach, and spent the rest of his days weeping prostrate over the grave of his victim.
According to the Karaite Jewish sage Moses b. Elias Bashyazi, Judah benTabbai was the founder of Karaite Judaism.