Equal-channel angular pressing (ECAP) experiments were conducted on a Mg-12Al-0.7Si magnesium alloy to investigate the influence of extrusion pass on its microstructure and mechanical properties. Homogeneously refined grains and secondary Mg17Al12 particles have been observed after multiple pass ECAP processing at 573 K. Mg2Si phase with size of about 2~3 μm has been observed after 8-pass ECAP processing; its morphology changes from initial coarse Chinese script shape to fine granule polygonal shape and its distribution tends to dispersing. The ultimate strength and the elongation of the alloy at room temperature remarkably increase to 293 MPa (after 6-pass processing) and 5.1% (after 8-pass processing), respectively. During the high temperature (200 °C) test, 2-pass processed specimen exhibits high strength of 204 MPa, and the 6-pass processed specimen has better elongation of 34.4%. The high strength of ECAPed alloy is attributed to grain refinement and modification of the second phase during ECAP, especially the Mg2Si phase. It is also shown that the basal plane texture (0002) developed by repetitive ECAP pressing influences the mechanical behavior of the ECAP-processed alloy