The solvent extraction method was used for the recovery of molybdenum from the spent HDS (Hydrodesulfurization) catalysts. The required experiments were designed by RSM (Response Surface Methodology) method according to CCD (Central Composition Design), and four independent parameters were examined. The value of Mo recovery in different conditions showed that the effect of the leach solution acidity is insignificant at a low concentration of Cyanex 272. The optimum value for Cyanex 272 concentration, H+ concentration of leach solution, temperature, and Mo concentration was obtained 0.27 M, 3.4 M, 30 ˚C, and 279.74 mg/L, respectively. The Mo recovery was 99.05% in these conditions, which had 0.74 error from the software predicted value.