SiC/Al composites were fabricated by pressureless infiltration technique using the silicon carbide powder and aluminum alloy as the starting materials. The phase, microstructure and mechanical properties of the sample were characterized by SEM, XRD and universal testing machine. The results showed that the SiC/Al composite was infiltrated completely by aluminum alloy. The microstructure of the sample was homogeneous. No obvious pores were detected. The major phases of SiC/Al composites were SiC and Al. Othe weak XRD characteristic peaks such as Si, Mg₂Si and MgAl₂O₄ phase were also observed in SiC/Al composites. The soaking property of liquid Al could be enhanced by the addition of Mg into aluminum alloy. Compared with The composites of 7 Mg, the composites of 10 Mg have higher dentity and better structure. Composites showed the characteristics of brittle fracture. SiC particles were destroyed by the way of transcrystalline cleavage.