Abstract. In Thailand, the iron and steel industry is one of the major industries to provide raw materials to other ones. In order to heat a billet to a proper temperature, it is fed into a reheating furnace, which generates heat by the combustion of fuel from direct-fired burners. After the temperature uniformity of the billet is achieved, it will be sent to the rolling process. The major mechanism of heat transfer in the reheating furnace is the thermal radiation because of the high combustion gas temperature. The temperature distribution of a billet subjected to the thermal radiation of the enclosure surfaces in a reheating furnace is presented in this study. The 2-D steady-state heat conduction equation is numerically solved by the finite volume method together with the Gauss-seidel iterative technique. A qualitative agreement between the numerical result and the data from filed measurement is presented. The variations of the temperature uniformity of the billet with different insulation thicknesses, flame temperatures and furnace floor temperatures are investigated. The result indicates the hot spot at the middle of billet originated from the position of combustion flame. When the wall insulation thickness is decreased, the thermal radiation of combustion flame is decreased, leading to the higher degree of the temperature uniformity of the billet. In case of the lower flame temperature or the higher the floor temperature, the degree of the temperature uniformity of the billet also increases.