Abstract: Antioxidant is one of the most important additives in lubricating oils, among which the asymmetric hindered phenol antioxidant is a hot research topic in recent years. As a new kind of high efficiency antioxidant, it has been applied gradually and achieved better effect than the traditional hindered phenol antioxidant. Asymmetric hindered phenol 2-tert-butyl-5-pentadecylphenol was synthesized from 3-pentadecylphenols and tert-butyl chloride by alkylation process. The structure of synthetic product was characterized and its antioxidant properties in mineral base oil and synthetic base oil were investigated. The results showed that the 2-tert-butyl-5-pentadecylphenol has advantages of strong oxidation resistance and good sensitivity in synthetic base oils，and its comprehensive performance was better than the commonly used hindered phenol lubricant antioxidant.

Key words: antioxidant, asymmetrical hindered phenol, 2-tert-butyl-5-pentadecylphenol, synthetic base oil