The authors developed the optimum thin film thermocouples in terms of materials, shape and dimensions to make instantaneous surface temperature and heat flux measurements of combustion chamber wall in internal combustion engines with accuracy by the computer analysis. And they succeeded to make thin film thermocouple in ceramic piston, by the application of the above technique. Then, the instantaneous surface temperature was measured to obtained the instantaneous heat flux on the ceramic plate fixed on top of the piston. As a result, the following interesting phenomena have been obtained. (1) Contrary to their expectation, amount of heat transfer into the piston surface during combustion period on the ceramic wall is larger than on a conventional Al-alloy wall. (2) It is found that the ceramic wall of the combustion chamber can not decrease in cooling loss during combustion, so the engine out put does not increase except by use of turbocompound device. (3) The overall heat transfer on the ceramic wall in a cycle is, however, smaller than on the conventional Al-alloy wall since more heat flows backward from high temperature wall to the low temperature air in combustion chamber during in intake and compression strokes.