The effects of Beryllium (Be) on the microstructure and mechanical properties of Al–15%Mg 2 Si composite were investigated. The results showed that with the increase of Be content, the average size and volume fraction of primary Mg 2 Si particles decreases. Pseudo-eutectic Mg 2 Si has mainly a fine fibrous structure in both specimens with and without Be. However, in the samples containing Be, the path for crack propagation along cell boundaries is very tortuous. Meanwhile, β Al–Mg–Be phase based on a β-Al 3 Mg 2 phase of the Al–Mg system was observed in specimens containing Be. It was found that with the addition of Be the ultimate tensile strength (UTS) and elongation values improved. A study of the specimen's fracture surfaces via scanning electron microscope revealed that Be increases the number of fine dimples and decohered Mg 2 Si particles.