The distribution coefficients of thorium and radium between molten LiF-BeF2 and liquid bismuth solutions were measured at 600°C in support of the processing of the molten-salt breeder reactor (MSBR) fuel The increasing mole fraction of LiF in the salt phase from 40 to 70 mol% resulted in the rapid decrease of the distribution coefficient of thorium and in the slow decrease of that of radium. A comprehensive correlation of distribution behavior with salt composition is given by taking into account the formation of complex ions. The equilibrium distribution data affirm that thorium and radium exist mainly as Li2ThF6 and RaF2, respectively, in the salt phase. It is suggested that the lower mole fraction of LiF in the fuel salt is effective in the MSBR fuel processing.