The microstructure evolution and mechanical properties of magnesium alloy AZ31D processed by equal channel angular extrusion(ECAE) are studied. The processing temperature and the passes of extrusion are important factors to affect the microstructure and mechanical properties of the magnesium alloy during ECAE. In this paper, ECAE was performed at the temperature from 523 to 673K. The ductility increased through the grain refinement after the ECAE because the recrystallization took place and high angle grain boundary formed. The elongation of magnesium alloys AZ31D was improved after the ECAE. The maximum elongation-to-failure of magnesium alloys AZ31D processed by ECAE for 4 passes at 573K and strain rate of 0.5 10−4 s−1 × was 350%.