We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/A13003 was 38, which was larger than 21.39 of Cu/AI(Cu/pure Al). It was because that the difference of flow stress between copper as the sheath material and A13003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/A13003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/A13003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/A13003 was higher than that of Cu/Al under the same extrusion conditions.