Menachem Mendel Yosef Zaks (Hebrew: מענדיל זאקס; 1898–1974) (commonly known as Rabbi Mendel Zaks) was an Orthodox Jewish rabbi in Belarus and the United States, best known for being the Rosh Yeshiva of the Raduń Yeshiva and being the son-in-law to Yisrael Meir Kagan, the Chofetz Chaim.

He was forced to leave Radun during World War I and then studied under Reuven Dov Dessler.

In 1922, he married Faiga Chaya, Kagan's youngest daughter (who was 64 at the time of her birth).

Legend has it that Zaks edited the final version of the Mishnah Berurah in his office (currently occupied by Dr. Seth Taylor) in the MTA building.

Zaks had an extraordinary memory, a pure mind, and was an expert in the Talmud and its commentaries.