A novel voltammetric method using the PEDOT (poly(3,4-ethylenedioxy)thiophene) modified electrode was developed for simultaneous measurement of various combinations of dopamine (DA) and ascorbate anion (AA). Both the cyclic voltammetry (CV) and square wave voltammetry were used for the measurement of neurotransmitters by means of the PEDOT modified electrodes. Well-separated voltammetric peaks were observed for dopamine and ascorbate anion at the PEDOT modified electrodes with peak separation of 0.170V. The electrostatic interaction between the heteroatom of PEDOT film and ascorbate anion was confirmed by adsorption of molybdate ions. A hydrophobic interaction was existed between the aromatic part of dopamine and the PEDOT film. The RRDE (rotating ring disk electrode) method was applied to study the redox reaction mechanism of dopamine and ascorbate anion. The Levich plot indicated that the electrocatalytic reaction between ascorbate anion and dopamine was mass transfer-controlled. The value of ‘diffusion co-efficient’ of dopamine and ascorbate anion were calculated to be 6.1×10−6 cm2 s−1 and 9.2×10−6 cm2 s−1.