A boundary layer analysis is presented to investigate numerically the effect of radiation on natural convection flow of an optically dense viscous fluid over an isothermal truncated cone in this paper. The nonsimilar governing equations are obtained by using a suitable transformation and solved by the Keller box method. Numerical results for the dimensionless velocity profiles, the dimensionless temperature profiles, the local friction coefficient and the local Nusselt number are graphically presented for the dimensionless distance xi, the Prandtl number Pr = 0.7, the radiation-conduction parameter R-d and the surface temperature parameter H. It is shown that increasing xi, R-d and H increases the local Nusselt number. The local friction coefficient decreases with increasing the above three parameters. Whereas, for the larger value of R-d and H, the variation of the local friction coefficient with xi has the phenomenon of maximum. Furthermore, the local friction coefficient and the local Nusselt number of the truncated cone approach those of the inclined plate (full cone) for the case of xi=0 (xi --> infinity).