A glassy carbon electrode modified with GR/Au nanocomposites was prepared for the simultaneous determination of isoniazid(INZ) and ascorbic acid(AA).In 0.1 mol?L-1 PBS(pH 3.5) buffer solution,the electrochemical behaviors of INZ and AA were investigated by cyclic voltametrmy(CV).The results indicated that the anodic peak currents of both INZ and AA showed linear relationships with the square root of scan rate over a wide range of 50-300 mV?s-1.Furthermore,the nanocomposites modified electrode showed an efficient catalytic role in the electro-oxidation of INZ and AA,leading to a remarkable peak resolution(ΔV=170 mV) between the two compounds.Under the optimal experimental conditions,the anodic peak currents were linear over ranges of 3.0×10-6-1.5×10-4 mol?L-1 for INZ and 3.0×10-5-1.0×10-3 mol?L-1 for AA,with detection limits of 8.0×10-7 mol?L-1 and 6.0×10-6 mol?L-1,respectively.The proposed method was successfully applied in the determination of INZ and AA in commercial drugs.