Electrochemical polymerization was carried out in a one-compartment cell containing deaerated acetonitrile, and 100 mM tetrabutylammonium tetrafluoroborate monomer of 3-methylthiophene. The polymer films were grown on a gold electrode by bulk electrolysis at 1.700 V (vs. Ag/Ag+). The modified sensor showed an excellent electrocatalytic effect towards oxidation of the mixture of 3,4-dihydroxyphenylacetic acid (DOPAC), ascorbic acid and uric acid, which appeared at a pH range of 2-11 by differential pulse voltammetry (DPV) techniques. The best results for determination of DOPAC were obtained by DPV in PBS (pH 7.00). A calibration curve was obtained in the DOPAC concentration range of 1.0-50.0 mu M (r = 0.9948). Limit of detection and limit of quantification were found as 0.066 mu M and 0.220 mu M, respectively. The results of the experiments indicated that the sensor has good stability, sensitivity and reproducibility for at least one month if stored in dry air.