Abstract: This invention relates to piston compression ring assemblies, each of which consists of a main ring element and an auxiliary ring element. The assemblies can by themselves adjust the radial gaps between the assemblies and the liner, and the gaps between the assemblies and the liner, and the gaps between the assemblies and the wall of the ring groove in the piston. The two ring elements engage with each other on their flat sides, and there is a notch for accommodating lubrication oil provided in the engaging portion. The radial cuts in each ring element stagger each other by an angle of 180.degree.. The two ring elements are good sealing and lubricating, respectively, therefore they can reduce the leakage of gas and the compensation of oil, and have a long period of use. They can thus improve the efficiency and the power of internal combustion engine, and reduce the emission and the noise of the internal combustion engine.