Old Mosque, Ottoman-era mosque and museum in Stara Zagora, Bulgaria.

The Old Mosque is an Ottoman-era structure in Stara Zagora featuring a rectangular prayer hall and traditional design elements from that period. Inside, archaeological collections from different time periods are displayed, documenting the region's history.

Built in 1408/09 on the orders of Emir Hamza Bey, apparently an Ottoman governor of Stara Zagora, during the interregnum struggles of 1402–1413. Repaired in 1789–90, it was damaged in the Russo-Turkish War of 1877–78 when its minaret was destroyed. After restoration in 2008–2013 it became the Museum of Religions.

The building is known as Eski Cami (Old Mosque) and Hamza Bey Mosque, after the Ottoman governor who ordered it built in the early 15th century. Since 2013 it has housed the Museum of Religions, whose exhibits present the different faiths practised in the region. Look for the Arabic stone inscription above the inner door.

The museum occupies the former prayer hall and the northern portico with its three small domes; the mihrab niche sits in the thickness of the south wall, opposite the entrance. The minaret that once rose at the northwest corner was demolished in the mid-1980s, so the dome now stands bare. The building was restored in 2008–2013 with European Union funding.

The dome, 17.47 m across, rests directly on the walls of the square prayer hall without intermediate supports, which makes it the second-largest single-domed mosque of its kind after Bayezid I's Mudurnu mosque of 1388. A Turkish bath once stood immediately to its east, as at Mudurnu.