PURPOSE: To dispense with use of precious spheroidal graphite cast iron by using vermicular graphite cast iron as ring in case the strength is insufficient in ring made of flaky graphite cast iron.

CONSTITUTION: Vermicular graphite cast iron is used as ring material. As said cast iron, e.g. that contg. by weight 3.3W4.0% C, 2.0W3.0% Si, 0.3W1.0% Mn, 0.2W0.6% P, ≤0.1% S as general components, 0.01W0.05% Mg as spheroidizing agent further one kind or more among 0.1W0.2% Ti, 0.01W0.04% Cr, 0.01W0.1% B as agents for improving wear resistance is exemplified. If in cast strength of piston ring made of flaky graphite cast iron is slightly insufficient, use of that made of spheroidal graphite cast iron as conventional is made unnecessary, and piston ring made of vermicular graphite cast iron can be used.