The effects of SiC particle size and alloy elements such as Si, Cu and Ti on the response to aging treatment and wear resistance in Al-5Mg-X(Si,Cu,Ti)/SiCp composites fabricated by pressureless infiltration method have been investigated by hardness tester, scanning electron microscope (SEM), X-ray diffractometer (XRD), differential scanning calorimetry (DSC) and wear tester. The Al-5Mg-0.3Si-0.1 Cu-0.1Ti/SiCP composites had better wear resistance property among Al-5Mg-X(Si,Cu)/SiCP composites. The wear resistance property of all the composites was enhanced after aging at 170degreesC for 8 hrs due to precipitates of beta'(Mg2Si) phase. The wear resistance property of the composite as-fabricated with 50 mum size of SiC particle is superior to that of the composite as-fabricated with 100 mum SiC size of particle. In Al-5%Mg alloy aged at 170degreesC for 8 hrs, the frictional seizure appeared more than abrading speed of 1.90 m/s, but in Al-5Mg-(Si,Cu,Ti)/SiCP composites aged at 170degreesC for 8 hrs, the frictional seizure was not found at abrading speed ranging from 0.5 m/s to 4.3 m/s.