Basasiri (died 1059) was a Turkish slave who rose to become a general in Iraq, and staged a revolt against the Seljuks.
Basasiri had been a favorite of the Buwayhid amir al-Malik al-Rahim. When the Buwayhids were expelled from Iraq by the Seljuks in 1055, Basasiri began a rebellion against their authority. The fighting dragged on for a few years with neither side able to gain a definitive advantage over the other. Basasiri eventually turned to the Fatimids for aid. They provided the necessary help and appointed him as Fatimid viceroy of Iraq.
With the support of the Mesopotamian Arabs, Basasiri managed to take Baghdad at the end of 1058. The Caliph al-Qā'im was removed from the city and confined at Haditha and the Fatimids were mentioned in the Friday prayers. When the Seljuk ruler Toghrïl Beg marched on the city, however, Basasiri lost support. His rebellion collapsed, and was forced to flee Baghdad about one year after capturing it. His flight was useless, however, as he was killed in a nearby skirmish.