The Church of Saint Demetrius, or Hagios Demetrios is the main sanctuary dedicated to Saint Demetrius, the patron saint of Thessaloniki (in Central Macedonia, Greece), dating from a time when it was the second largest city of the Byzantine Empire. It is part of the site Palaeochristian and Byzantine Monuments of Thessaloniki on the list of World Heritage Sites by UNESCO since 1988.

The basilica is famous for six extant mosaic panels, dated to the period between the latest reconstruction and the inauguration of the Byzantine Iconoclasm in 730. These mosaics depict St. Demetrius with officials responsible for the restoration of the church (called the founders, ktetors) and with children. An inscription below one of the images glorifies heaven for saving the people of Thessalonica from a pagan Slavic raid in 615.