A systematic study of solvent extraction of molybdenum(VI) and tungsten(VI) from hydrochloric acid media using neutral phosphine oxide extractant, cyanex-923 in toluene has been performed. These metal ions are quantitatively extracted with cyanex-923 in toluene in the acidic range 5-7 M, and from the organic phase they are stripped with 1.0 M NaOH. The effect of pH, equilibrium period, diluents, diverse ions and stripping agent on the extraction of Mo(VI) and W(VI) has been studied. The extraction reactions proceed by solvation and the probable extracted species in the organic phase were MoO(2)Cl(2)center dot 2Cyanex-923 and WO(2)Cl(2)center dot 2Cyanex-923. Based on these results a sequential procedure for their separation from each other has been developed.