In the present paper, the author tried experimentally to determine the heat transmission coefficient of inclined rectangular plate immersed in the free and forced streams. Two plates sizes of which are 100×100×11 and 200×200×11 respectively were taken, and the experiment was carried out over the ranges of temperature differences 0 to 100°C and as air velocities 6.40 to 23.0 m/s. From the results of experiments the eleven data have been obtained graphically, and these graphs sufficiently represent the differences due to inclinations.