Yaakov Ben Zion Mendelson (Yiddish: יעקב בן־ציון הכהן מענדעלסאׇן) (October 12–14, 1875 – August 5, 1941)[note 1] was a Russian-born Orthodox Jewish scholar and rabbi.

The former encouraged him to study under the Rogatchover Gaon, Rabbi Joseph Rosen, from whom Mendelson later received rabbinic ordination.

Shortly after his ordination, he was betrothed to a cousin, Feiga Skuy, but his marriage was postponed when he was drafted into the Russian Army, known for its mistreatment of Jewish conscripts.

In 1921 he was appointed Chief Rabbi of Newark, with primary jurisdiction over matters of shechita and kashrut, which position he held until his death.

[7] Mendelson was an active member of Knesseth ha-Rabbanim,[8] where he was regarded as an expert in kashrut, and played a prominent role in its conventions.

His son, Harry Morein (né Mendelson), was a founder of the Young Israel of Newark, and an early advocate to change New Jersey's Sunday blue laws.