Provided is a piston ring capable of maintaining an excellent effect of preventing aluminum cohesion in a high output engine over a long period of time. At least one of the upper, lower, and side faces of the piston ring is coated with a silica-based coating in which hard nanoparticles are dispersed. The coating has a Martens hardness of 1,000 to 8,000 N/mm2. As the hard nanoparticles, carbon nanoparticles, nanodiamond particles, carbon nanotubes, or carbon nanofibers are used. To the coating, resin particles of a fluorine-based resin or a polyether-based resin may be added.