To provide a piston ring superior in side surface sealability and stick resistance of upper-lower surfaces of a ring groove of a piston and upper-lower surfaces of the piston ring, and superior in follow-up performance to a cylinder wall.

This invention provides the piston ring further superior in the follow-up performance to the cylinder wall, by securing the side surface sealability and the stick resistance with the upper-lower surfaces of the ring groove 5 of the piston, by contacting in a state of generating proper pressure between the ring groove 5 of the piston 4 and the cylinder wall 7 when operating the piston by elasticity and a shape of a ring body 1 composed of resin, a rail member 2 and a tension ring 3.