A conventional extrusion has been carried out to induce significant grain refinement in Mg-Zn-Y-Zr alloy. The results showed that good superplasticity have obtained in this extruded alloy. The simple and rapid processing route may allow it to be put into successfully practical use in industry. The effects of temperature and strain rate on superplastic deformation of the extruded alloy were studied. The optimum condition with the elongation of more than 450% was found to be at 450°C and 3.3×10-4s-1. Jump tests were carried out at 300-450°C and 8.3×10-5 ~ 1.7×10-2s-1. The activation energy for superplastic deformation at 300-450°C is 106kJ/mol and the stress exponent is about 2.8. The superplasticity observed in this studied condition may be attributed to mechanisms of dislocation creep mainly within large grains and grain boundary sliding (GBS) of small grains.