PURPOSE: To form a thick chromium plating and to obtain a durable piston ring by providing a wide groove on the sliding surface of a ring sliding surface before a chromium plating is applied, and then providing plural layers of chromium platings thereover.

CONSTITUTION: Prior to the application of chromium plating, a groove 4 is processed mechanically on the sliding surface 1b of a piston rig 1 beforehand, and the first round of chromium plating 2a is applied to bury the groove 4. After that, a ring sliding surface 2c is finished by a mechanical process, the second round ohromium plating 2d is formed over the surface, and the final finish is carried out to form a thick chromium plating which could not be formed in the conventional way. As a result, a reliable thick chromium plating layer can be formed.