Microstructural evolution and mechanical properties of Al-12Si alloy subjected to equal-channel angular extrusion (ECAE) were investigated. The high stresses imposed in ECAE led to the fragmentation of the needle-shaped eutectic silicon plates into smaller particles. The length and width of the Si particles decreased from 35.5 +/- 31.8 mu m and 13.7 +/- 8.9 mu m without ECAE to 2.7 +/- 1.1 mu m and 1.3 +/- 0.4 mu m after six ECAE passes, respectively. The average aspect ratio of 3.2 +/- 1.8 for the Si particles in the as-cast condition decreased to 1.18 +/- 0.8 after six ECAE passes with a corresponding increase in the average roundness of 0.26 +/- 0.19 to 0.61 +/- 0.19. ECAE increased the strength, ductility, and impact toughness of the alloy. The increase in the tensile and yield strengths after six passes was about 68 % and 100 %, respectively. The alloy after six ECAE passes exhibited 12 % elongation to failure, which was almost eight times higher than that of the as-cast alloy. The absorbed energy increased with an increase in the number of passes, finally reaching 11.5 J/cm(2) after six passes, which is about four times higher than that of the as-cast alloy.