The purpose of this study was to develop lightweight hat shaped section side members which absorb the most of the energy during the front-end collision of vehicle. The hybrid side member was manufactured by combination of aluminum and CFRP. An aluminum or CFRP (Carbon Fiber Reinforced Plastics) member is representative lightweight materials but its axial collapse mechanism is different from each other. The aluminum member absorbs energy by stable plastic deformation, while the CFRP member absorbs energy by unstable brittle failure with higher specific strength and stiffness than those in the aluminum member. Based on the respective collapse characteristics of CFRP side and aluminum members, the hybrid side members were tested on the axial collapse loads to get a synergy effect when the member is combined with the advantages of each members, such as energy absorption by the stable folding deformation of the aluminum member and by the high specific strength and stiffness of the CFRP member. Energy absorption capability and collapse mode of the hybrid side members were analyzed.