The Mosque of Ibn Tulun (Arabic: مسجد إبن طولون, romanized: Masjid Ibn Ṭūlūn) is a historic mosque in Cairo, Egypt. Built between 876 and 879 by its namesake, Ahmad ibn Tulun, it is the oldest well-preserved mosque in Egypt. Its design was inspired by the 9th-century mosques of Samarra in Iraq, the Abbasid capital at the time, making it an important representative of classical Abbasid architecture. Today, it is one of the most significant monuments of Islamic architecture in Egypt.

The mosque consists of a large open courtyard surrounded by roofed sections that are divided into aisles by rows of pointed arches. The arches are decorated with carved stucco, though not all of the original decoration has been preserved. The mosque is surrounded by an outer enclosure, the ziyada. The minaret, which has an unusual form with an external spiral staircase, stands in this enclosure. Various additions and restorations were made after the 9th century, including an important renovation by the Mamluk sultan Lajin in 1296. The present-day fountain and domed kiosk in the center of the courtyard date from this restoration. In addition to the main mihrab (niche symbolizing the direction of prayer), the prayer hall contains several flat stucco mihrabs added in different periods. After a period of severe neglect in the 19th century, during which the building was converted to other uses, the mosque was restored in the 20th century.