A new ester-phenolic antioxidant based on dipentaerythritol was synthesised via a series of esterification reactions. The first esterification of dipentaerythritol with 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was carried out, and then the second esterification affords the final ester-phenolic antioxidant by the reaction of the first esterification intermediates with isostearic acid. This antioxidant is functional complex which can act as not only antioxidant but also synthetic ester lubricant. The ester-phenolic antioxidant was characterised with Fourier transform infrared spectroscopy (FTIR), rotary bomb oxidation test (RBOT) and thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis. The FTIR analytical results confirmed the chemical structure of the as-synthesised antioxidant. RBOT demonstrated that this phenolic antioxidant has excellent antioxidant efficiency. The analytical results of TG/DSC showed that this antioxidant had low volatility and good thermal stability.