We measured what the torque changed as driving a Wankel engine by means of burning L.P.G. and varying the timing of spark plugs. We seeked the best spark plug timing and the characteristic of ignition advance from the experimental results. Further we measured the change of torque when varying the air-fuel ratio. The torque was compared the case of using L.P.G. with the case of using gasoline. From the results, it has been made clear that was followed; The characteristic of mechanical spark advance of T-spark plug is similar to the case by means of burning gasoline. But L-spark plug needs to advance the angle from 5°to 10°for sparking as compared with case by gasoline. As the speed being higher,both L and T-spark plug timings tend to retard somewhat. On the characteristic of vacuum spark advance,the case by L.P.G. has smaller advanced degree than the case by gasoline. B.T.D.C. of L-spark plug arrive to 30°which is maximum value as like as the case by gasoline. The limit value of air-fuel ratio for operating acceptably is about 24 which is pretty large as compared with the case by gasoline.The torque of the case by L.P.G. is something less than the case by gasoline.