The Great Mosque of Mahdiya is a mosque that was built in the tenth century in Mahdia, Tunisia. Located on the southern side of the peninsula on which the old city was located, construction of the mosque was initiated in 916, when the city was founded by the Fatimid caliph Abdallah al-Mahdi, to serve as the new city's main mosque. Most of the Fatimid-era city and its structures have since disappeared. The current mosque was largely reconstructed by archeologists in the 1960s, with the exception of its preserved entrance façade.

The Fatimid architecture that developed in the Fatimid Caliphate (909–1167 CE) of North Africa combined elements of eastern and western architecture, drawing on Abbasid architecture, Byzantine, Ancient Egyptian, Coptic architecture and North African traditions; it bridged early Islamic styles and the medieval architecture of the Mamluks of Egypt, introducing many innovations.