Mordecai belonged to which tribe of Israel?

Answer: Benjamin

Mordecai son of Jair, son of Shimei, son of Kish, was a Jewish man from the tribe of Benjamin living in Susa.

“Now there was at the citadel of Susa a Jewish man from the tribe of Benjamin named Mordecai son of Jair, the son of Shimei, the son of Kish.”— Esther 2:5 (BSB)