AZ31 alloy sheets were produced by twin-roll casting (TRC) and sequential hot rolling. Uniaxial tensile tests were used to evaluate the deformation properties of the AZ31 alloy at a strain rate of 7×10-4s-1 and a temperature range from room temperature to 400°C. The microstructure evolution and fracture behaviour were observed by optical microscopy and scanning electronic microscope. The results show that the elongation of the AZ31 alloy increases with increasing temperature at a strain rate of 7×10-4s-1. The AZ31 alloy begins to exhibit superplasticity at 300°C. The elongation of 497.8% is achieved at 400°C. The deformation of the AZ31 alloy at low temperature is controlled by dislocation motion, and with increasing temperature (above 300°C), grain boundary sliding (GBS) begins to play a dominant role during superplastic deformation.