Sekbanbaşı Mosque was a mosque located in the Ottoman capital of Constantinople (modern-day Istanbul). It was originally a Byzantine church. According to the writings of Hafiz Hüseyin al-Ayvansarayî (Hadîkatü’l-cevâmi‘), the original Byzantine church had been converted by İbrahim Ağa (died 1496–7), the lieutenant of the Ottoman sekban regiments (sekbanbaşı). The building was located in Kendir Sokağı, in the Kırkçeşme quarter (Fatih district), near the ancient aqueduct of Roman Emperor Valens.