The microstructure and mechanical properties of Al-Mg2Si alloys by equal channel angular pressing (ECAP) at 250 oC were studied. Vickers hardness and tensile testing show that the hardness, tensile strength and elongation of the alloys increase after ECAP for 4 passes. However, the hardness and tensile strength decrease after ECAP for 8 passes while the elongation increases further. SEM and TEM observations show that the original skelecton shape or the Chinese-script Mg2Si phase are obviously broken after ECAP. The more the extrusion passes, the more the fragmentated Mg2Si phase, and the more the alloys refining. The mechanism for the decrease in hardness and tensile strength of the specimen after ECAP for 8 passes compared with 4 passes was discussed.