Sterically hindered p-cresol oligomer was prepared by enzymatic polymerization in aqueous micelle system. Influences of p-cresol oligomer on thermaloxidation stability of polypropylene were investigated by TG, DSC and thermal aging test. In contrast with virgin PP, the initial oxidation temperature of PP stabilized with p-cresol oligomer increases by 32 ℃ and oxidation induction time increases by 27 min. Blend of p-cresol oligomer/PP shows good long-term thermal oxidation stability and hardly any decrease in the tensile strength is observed even after thermal aging at 140 ℃ under air atmosphere for 240 h. Investigations of thermal decomposition kinetics of PP and p-cresol oligomer/PP was performed by Flynn-Wall-Ozawa method. Result shows that the apparent activation energy of thermal degradation of PP is enhanced after blending with p-cresol oligomer.