The Ancient Synagogue of Barcelona (Catalan: Sinagoga Major de Barcelona, Spanish: Sinagoga Mayor de Barcelona, Hebrew: בית הכנסת העתיק מאיור) is believed to be an ancient synagogue located in the centre of Barcelona, Catalonia, Spain. It has been described as one of the oldest synagogues in Europe. After many centuries of use for other purposes, the building re-opened as a synagogue and museum in 2002. No congregation prays regularly at the Sinagoga Major, but it is used for festive occasions.
Archaeological investigations show that the original structure of the building was built in the third or fourth century; whether this structure was the synagogue cannot be said with certainty. The building was significantly expanded during the 13th century. Medieval Barcelona is known to have had several synagogues, and the main synagogue was certainly in the immediate area. King James I visited the synagogue in 1263 at the conclusion of the Barcelona Disputation. Shlomo ben Aderet served as the rabbi of the Sinagoga Major for 50 years.