The novel covalently modified glassy carbon electrode with polyethylene oxide has been prepared using an electroadsorption method for the simultaneous determination of dopamine (DA) and ascorbic acid (AA). This new electrode presented an excellent electrocatalytic activity towards the oxidation of DA and AA by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The separation potentials of the oxidation peak potentials for them were about 155mV in CV and 216mV in DPV. The differences are large enough to determine DA and AA individually and simultaneously. Calibration curves in the ranges of 5.0–40 and 300–1700μmolL−1 were obtained for DA and AA, respectively. The lowest detection limits (S/N=3) were 0.25 and 50μmolL−1 for DA and AA, respectively.