An experimental study for convective heat transfer from an open cavity has been made in the range of Reynolds numbers from 10 4 to 10 5 . The cavity model of which both depth and width are 25 mm is made of brass for the study of effect of temperature nonuniformity on the wall surface of the open cavity. The fluid temperature distribution in the open cavity is almost uniform except a thin portion immediately adjacent to the wall surface of the open cavity. The representative mean temperature of the fluid in the open cavity is used for the flowing treatment. The wall surface temperature distribution of the open cavity is as follows: the vertical wall surface temperature is decreased steeply from the bottom to the opening region of the open cavity. In the present paper, the average temperature of cavity wall surface is used for the flowing treatment. Convective heat transfer from the open cavity is treated by the following two phenomena: the heat transfer related to the temperature difference between the wall surface and the fluid in the open cavity; and the heat transfer related to the temperature difference between the fluid in the open cavity and the external main stream. Experimental data obtained for the open cavity which is made of brass coincide with the existing data obtained under the conditions that the wall surface temperature distribution is almost uniform.