The purpose of this research is to clear the effect of fiber-reinforced metal (FRM) on strength of pistons reinforced by FRM. First, the finite element model of a simplified piston of gasoline engines was constructed. Stress analyses were performed using the proposed model, in the case that combustion pressure was loaded to the piston made of aluminum alloy (AC8A). Stress analyses of the piston composed of aluminum alloy (AC8A) and FRM were also performed. The effect of FRM on strength of pistons was discussed using the results of stress analyses.