The Mosque of Ahmad Ibn Ţūlūn (Arabic: مسجد أحمد بن طولون‎) is located in Cairo, Egypt. It is arguably the oldest mosque in the city surviving in its original form, and is the largest mosque in Cairo in terms of land area.

The mosque was commissioned by Ahmad ibn Ţūlūn, the Abbassid governor of Egypt from 868–884 whose rule was characterized by de facto independence. The historian al-Maqrizi lists the mosque's construction start date as 876 AD[1], and the mosque's original inscription slab identifies the date of completion as 265 AH, or 879 AD.