Sixteen electrochemical electrodes were prepared by modifying the electro-polymerized 3-methylthiophene to the below and above of the single-walled carbon nanotubes (SWCNTs) dispersion that dripped onto glassy carbon electrode. Determination of benserazide (BS) and levodopa (LD) in the presence of ascorbic acid (AA) was performed by differential pulse voltammetry (DPV) technique to find out which of these electrodes gave the best and fastest simultaneous response. The highest resolution and current densities were achieved with the electrode that 20 mu L 1.0% SWCNT was dribbled onto the bare electrode. The morphology and structure of modified electrode were characterized by scanning electron microscopy. Under optimum conditions AA, BS and LD gave sensitive oxidation peaks at nearly 90, 210 and 320 mV, respectively. The oxidation currents increased linearly with concentration of BS (50-100 mu M) and LD (5.0-9.5 mu M) in phosphate buffer solution (pH 7.0). The detection limits obtained by DPV were 3.0 mu M for BS and 1.1 mu M for LD. Additionally, the proposed modified sensor was applied successfully to biological fluids and tablet samples. The results proved that the modified sensor showed excellent selectivity, repeatability and reproducibility with high stability and accuracy.