Cyclic combustion variation factors in the light-load operation of the two-point ignition rotary engine have been clarified by statistically analyzing the relationship between the heat release pattern for each cycle and the indicated mean effective pressure on the combustion by the individual spark plugs. As a result, combustion variation phenomenon was found to be mainly caused by combustion variation in the region shifted from the leading side spark plug to the trailing side. This is attributable to variations in flame propagation going from the leading side spark plug to the trailing side, and to large variation in heat releasing start time by the trailing side spark Plug.As factors affecting the ignitability of the spark plug on the trailing side, temperature, mixture composition and gas velocity were examined. It was confirmed that the conventional notion concerning the poor ignitability of the trailing side spark plug being due to the poor scavenging of the combustion gas in the spark plug hole does not hold. Rather it was found that the main cause is that since the spark plug is surrounded by the wall, the formed flame kernel is cooled and its growth hampered.