The Defterdar Mosque, or in long form the Defterdar Mahmut Efendi Mosque (Turkish: Defterdar Camii, Defterdar Mahmut Efendi Camii), is a historical mosque located in Eyüp, Istanbul, Turkey. It was commissioned by Defterdar Nazlı Mahmut Efendi (c. 1500-1546) and built by architect Mimar Sinan in 1542 ("defterdar" was the head of the financial department in Ottoman Empire).