Abstract: With RSiC ceramics of different porosities (17%, 23%, 28%, 34%) as substrate and ZL102 Al alloy as second phase, the Al/RSiC composites were prepared by vacuum pressure infiltration method and the effects of the porosities of RSiC ceramics on their properties were investigated. The results show that the Al/RSiC composites had the co-continuous three-dimensional interpenetrating network structure, meaning a continuous distribution of ceramics and metal phases in three-dimensional space. When the porosity of RSiC ceramics decreased from 34% to 17%, the bending strength of the composite first increased slightly then decreased, and reached the largest value of 181 MPa with the ceramics of 28% porosity. The thermal expansion cofficient of the composite decreased with the decrease of ceramics porosity and was below the theoretical calculation value. The three dimensional network structure of RSiC ceramics played a decisive role on the thermal expansion cofficients of the composites.