The electrochemistry behavior of dopamine was investigated by cyclic voltammetry and differential pulse voltammetry at a poly (gallic acid) film modified glassy carbon electrode. Two electrons and two protons participated in the diffusion-controlled electrocatalytic oxidation of dopamine with a diffusion coefficient of 2.186 × 10~(-5) cm~2/s. The interference of ascorbic acid with the determination of dopamine could be efficiently eliminated. This work provided a simple approach to selectively and sensitively detect dopamine in the presence of high concentration of ascorbic acid.