Workers removed dried weeds from inside the mosque and restored fittings. The mosque was built by the Mamluk Sultan al-Zahir Baybars bin Abdullah Al-Bindakari between 1266 and 1268.
Work to restore the mosque began in 2007, but stopped in 2011, the year protesters took to the streets and toppled autocrat Hosni Mubarak.
Egypt has struggled to fund restoration projects since then, as years of street unrest, political upheaval and militant attacks drove away tourists and foreign investors.
Cairo has a wealth of historic buildings of architectural interest, from the ancient era of the pharaohs through the flowering of Islamic civilization. But many monuments are crumbling due to lack of funding and neglect.
The Antiquities Ministry said it expected to complete the 100 million Egyptian pound ($5.57 million) restoration project in 12 to 18 months.
($1 = 17.9400 Egyptian pounds)
Writing by Lena Masri; Editing by Peter Graff