Normally, the sterically hindered phenols and diphenylamines, used as antioxidants, are added into the base oil simultaneously in order to improve the antioxidant efficiency. In view of this, we have designed a new type of antioxidant which combined the two traditional antioxidants into one molecule with Schiff base. These novel Schiff base bridged phenolic diphenylamine (SPD) antioxidants have been prepared through a one-step synthesis method which is suitable for large-scale production. The thermal stability and antioxidant ability were examined by thermal gravimetric analyzer (TGA) and pressurized differential scanning calorimetry (PDSC), respectively. The results showed that they both had better thermal stability and antioxidant efficiency than the commonly used commercial antioxidants. Importantly, the formulation of SPDs with other additives also exhibited improved antioxidant performances, presenting good application potential in the lubricant industry.