In the recent development of internal combustion engine, considerable increase in speed and power has been accomplished. This achievement, however, brought up various problems due to the excessive temperature of engine parts, which becomes a crucial factor in engine durability. In the present paper, temperature measurement of a marine engine was investigated experimentally. The adapter is made to pull out a thermocouple through the safety valve hole of the engine. The thermocouple is welded on the surface of the cylinder cover to measure the average temperatures of the engine cylinder cover. Ceramic adhesive was used for preventing the affect of high temperature combustion gas. The cylinder cover temperatures of the engine were measured by means of surface welding method. As a result, average temperatures of the engine cylinder cover were successfully in the range of 85~335oC. In the present study, the surface welding method was confirmed from the temperature measurement of cylinder cover in an experimental engine, and can be applied to large-sized marine engine without damage.