Abstract: The Co₃O₄/GR/GCE modified electrode, which as a novel electrochemical sensor for determination of vanillin in food, was prepared by dropping graphene (GR) onto a glassy carbon electrode(GCE) and then electro-polymerized by Co(COOH)₂ by cyclic voltammetry in this work. The Co₃O₄/GR composite nanomaterials were characterized by scanning electron microscopy. Moreover, the experimental conditions were optimized. Results showed that, 8.0 μL GR solution (1 mg/mL) of coating amount, 20 electro-polymerization cycles of Co(COOH)₂ and pH=5 of 0.1 mol/L phosphate buffer solution were chosen as the best experimental condition. Therefore, vanillin had a good linear relationship in the concentration range of 0.1～80 μmol/L with the electrochemical sensor, and the linear equation was: I_p (μmol/L)=0.1518C+0.5103 (R²=0.997) with detection limit was 0.033 μmol/L (S/N=3). The method was applied to the determination of vanillin in biscuit samples with good recovery and RSD of 1.47%. The results indicated that the electrochemical sensor had high sensitivity and fabulous stability, which proved the feasibility of the electrochemical sensor in practical sample detection and had a wide application prospect.