In order to understand the relationship between the location of piston ring gap and instantaneous change of oil consumption during engine operation, the ring rotation and instantaneous oil consumption were measured simultaneously in a hydrogen fueled single cylinder spark ignition engine. A radioactive-tracer technique was used to measure the rotational movement of piston ring. Two kinds of isotopes(60Co and 192Ir) with different energy level were mounted to the top and 2nd rings to measure each ring's movement independently. The instantaneous oil consumption was obtained by analyzing CO2 concentration in exhaust gas.From the result of ring rotational movement, typical patterns of ring rotation were obtained as follows; Rotational movements are usually initiated by changing the operating conditions. Piston rings tend to rotate easily under low load condition. The rotation speed of ring usually ranged in 0.2∼0.4 rev/min for top ring and 0.5∼0.6 rev/min for 2nd ring. The cyclic variation of oil consumption was observed and its periodicity correlates well with that of ring rotation. The peak of oil consumption occurred when the top and 2nd ring gaps were located with a certain distance. Therefore, it was shown that the dynamic change of oil consumption is induced by the rotational movement of piston rings and the dominant factor is the relative position of each ring not the absolute position. In other words, oil consumption increases if the top and 2nd ring gap come close each other, and decreases if the distance between them becomes further.