Mayor Synagogue is a former synagogue in the Hasköy district of Beyoğlu, Istanbul, Turkey. According to historian Lorans Tanatar Baruh, the synagogue was built in the Byzantine era and was called Mayor because it was the largest in the neighborhood. According to an unspecified historian, however, the synagogue was built 300 to 500 years ago by Jews from Majorca. (According to historian Jak Deleon, in the 1950s there was a Mayorka Synagogue in Hasköy.)
The synagogue is now used as storage space, workshops, and a billiard parlor. In September 2009, artist Serge Spitzer chose this site for his installation Molecular Istanbul.