Abstract: High temperature compressive deformation of SiC_W/ AZ91 composite and unreinforced AZ91 magnesiumalloy was performed using Gleeble-1500 thermal simulator in the range of deformation temperature f rom 423 to723 K, st rain rate f rom 0.002 to 0.25 s ^-1 and maximum deformation st rain of 60 %. The compressive t rue st resst rue st rain curves were measured and hot deformation microst ructures were observed. St rain sof tening behavior ofcomposite is more obvious than that of unreinforced alloy because of the rotation and breakage of whiskers duringcompression. The st rain rate sensitivity exponent ( m) and apparent activation energy (Q) of both the SiC_W/ AZ91composite and AZ91 alloy increase with the increasing of temperature. The higher m value of the composite is considered to be resulted f rom the fine microst ructure due to the addition of SiC whiskers. The addition of whisker limit s the cross slip of dislocations and migration of grain boundary, which causes Q value of the composite higher thanthat of the unreinforced alloy. During the compression, dynamic recovery and dynamic recrystallization occur in boththe unreinforced alloy and SiC_W/ AZ91 composite.