To provide a piston ring capable of favorably controlling wear form of a ring channel.

This piston ring 14 mounted in the ring channel at the outer periphery of a piston is formed to have a two layer structure constituted by laminating an upper layer 17 and a lower layer 18 formed by materials having different coefficients of thermal expansion. Since this piston ring 14 is thermally deformed to have curved cross section in accordance with rise of temperature accompanying increase of engine load due to difference in coefficient of thermal expansion between both layers to adjust a contact condition with the mounted ring channel autonomically in correlation with engine load.