The Haci Özbek mosque, according to the inscriptive plaque (kitabe) above a window, was built by Haci Özbek bin Muhammed in 734 A.H., three years following the conquest of Iznik by Orhan I. It is a single-unit mosque composed of a square hall crowned with a dome eight meters in diameter. The drum of the dome is dodecagonal and adorned with band of triangular planes on the interior. The three-bay portico preceding the hall to the west was torn down in 1940 to allow for road expansion. Carried on columns with Byzantine capitals, this portico was roofed with a barrel vault to the south and a mirror vault on the north. In its place, an enclosed portico was added to the northern side of the building in 1959. A minaret was never built. Ornamental details of the interior have been lost under layers of plaster. The construction of the mosque is brick and rubble stone, with saw-toothed brick cornices at the top of walls and terra-cotta tiles on the brick dome.
Iznik tarih ve Müze Komitesi yayini. Istanbul: Kenan Matbaasi, 1943.
Ayverdi, Ekrem Hakki. Osmanli mi?mârîsinin ilk devri: Ertugrul, Osman, Orhan gaazîler, Hüdavendigâr ve Yildirim Bâyezîd, 630-805 (1230-1402). Istanbul: Baha Matbaasi, 1966.
Eyice, Semavi. Iznik: tarihçesi ve eski eserleri. Istanbul: Sanat Tarihi Arastirmalari Dergisi Yayini, 1988.
Kuran, Aptullah. The mosque in early Ottoman architecture. Chicago: University of Chicago Press, 1968.
Ötüken, S. Yildiz. Türkiyede Vakif Abideler ve Eski Eserler. Ankara: Vakiflar Genel Müdürlügü Yayinlari, 1972.
Yalman, Bedri. Iznik: Nicaea. Governorship of Bursa, Provincial Directorate of Tourism: Bursa, 1999.