Abstract: The new intermolecular complex antioxidant [3-(3,5-di-tert-butyl-4-hydroxy-phenyl)] propionyl phosphoric acid bisoctadecanol ester was synthesized from methyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)-propionate (MPC)，diethyl phophite and octadecanol. The influence of catalyst and its quantity，reaction medium and other reaction parameters were studied. FTIR and elemental analysis results confirmed that the product was the one as desired. The results showed that by using organo-tin compound as catalyst，under the optimum reaction conditions the yield of the product (melting point 47.7—49.2℃) can be up to 75%. The antioxidant presented excellent performance by the tests of oxidation induction time (OIT)，melt flow rate (MFR)，tensile strength and elongation when used in PP.