To provide a piston ring used as a pressure ring of an internal combustion engine and having excellent capability to follow a bore.

A diametrally independent metal piston ring 10 is composed of an outer peripheral ring 1 and a synthetic resin inner peripheral ring 2. The outer peripheral ring 1 has such a section that radial width thereof is substantially equal to its axial width, or slightly smaller than that. The inner peripheral ring 2 has both ends abutting against each other under a specified temperature, due to expansion heat, for causing radial stress to press the outer peripheral ring 1 in a radially outward direction.