This study presents an optimization methodology to obtain the uniform thermal conditions over the 3-D design body (DB) in 3-D radiant furnaces. For uniform thermal conditions on the DB surfaces, optimal temperature of the heater and the best location of the DB inside the furnace are obtained by minimizing an objective function. The radiative heat transfer problem is solved on the basis of the Monte Carlo method (MCM) to calculate the heat fluxes on the DB surfaces. The genetic algorithm (GA) is used to minimize the objective function defined based on the calculated and desired heat fluxes. The results indicate that thermal conditions on the DB surfaces are greatly influenced by the location of the DB and temperature of the heater. It is concluded that the introduced method is well capable to achieve the uniform thermal conditions on the DB surfaces by finding the optimal values for temperature of the heater and the best location for the DB inside the radiant furnace.