The Sultan Ahmet Mosque was built under the instruction of Sultan 1. Ahmet. The Architect of the mosque was Sedefkar Mehmet Aga. He begun to build the Mosque in 1609, and finished it in 1614. Inside the mosque, blue Iznik mosaics were used. This is why it is called the Blue Mosque. Until today, many restoration works were done. Especially in 1888-1895, restoration works were very impotant. After this restoration, the most important restoration was in 1988 1990. In this paper the last restoration work will be explained. The restoration works may be grouped under seven headings: 1Work on main dome, 2Restoration of the stained glass windows, 3Restoration of the wooden shutters, 4Repair of the floors, 5Disassembling the scaffolding and cleaning, 6Repair of outer stone wall, 7The dome's lead plating and care of the cupola Transactions on the Built Environment vol 39 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509