The piston temperatures of a Nissan-Automobile E-type 1200cc gasoline engine were measured with the thermocouples, of which the wires were passed through the combustion chamber and led to the stationary position. The influences of the piston speed, load, cooling water, ignition advance, knocking and mixture ratio upon the piston temperatures were measured. The following were worth noticing. (1) When the engine speed was 4500 rpm under full load, the maximum temperature was about 200°C at the center of the piston head. (2) When the ignition timing was advanced, the piston temperature proportionally ros. And specially when knocking occurred, its maximum temperature was 60°C higher than that in case of nonknocking and reached 260°C. (3) With weak mixture ratio, the temperature of exhaust gas rose, but there was little influence upon the piston temperature.