Abstract: Pretreated gold electrode was modified by self-assembling in 4-(3-pyridyl)-2-mercapto-imidazole (abbreviated as PMIZ) alcoholic solution.Electrochemical behaviors of ascorbic acid and quercetin at this modified electrode (or designated as PMIZ/AuE) were studied by cyclic voltammetry.It was found that the PMIZ/AuE showed catalytic effect towards both the reactions of ascorbic acid and quercetin at the electrode,and that in a solution containing both ascorbic and quercetin,a potential difference of 240 mV was observed between the oxidation peak potentials of these 2 compounds,when measured by 1st derivative linear scanning voltammetry.Based on these facts,a direct method for determination of quercetin in the presence of ascorbic acid was proposed.Linear relationship between values of 1st derivative of peak current (ip) and concentration of quercetin was found in the range of 2.0 to 200 μmol·L-1,with its detection limit (3S/N) of 1.0 μmol·L-1.Values of recovery found were in the range of 98.8% to 102.0%.