A galvannealed steel sheet superior in workability wherein the steel sheet is characterized by containing silicon in an amount no less than 0.8 mass % and retained austenite in an amount no less than 3% (in terms of packing factor) and the alloy zinc plating is characterized by containing Zn—Fe alloy crystal grains which exist in its surface layer and have a specific crystal grain size such that the longer side of a crystal grain is no larger than twice the shorter side of a crystal grain and the number of crystal grains with an average particle size no smaller than 4 &mgr;m is no more than 5 per 70×50 &mgr;m. The steel sheet with alloy zinc coating has good mechanical properties (such as total elongation) and good plating surface slidability.