Abstract: Deformation twinning of cast magnesium alloy AM60 was investigated by compression at room temperature with various deformation degrees from 3.3% to 24% and various deformation rates from 0.2 mm/min to 5 mm/min,respectively.Microstructure of the deformed samples examined by optical microscopy showed that thick twins exited in a few amount of crystals at the beginning of the deformation.The thin-long twins and the thick twins appeared at the end of the deformation,and they could be observed in almost all crystals.With increasing compressing rates,the yield strength,compressive resistance fracture strength and density of twins increased,and twins became thin.