The poly(bromothymol blue) film was prepared using a simple cyclic voltammetry method. Field emission scanning electron microscopy and electrochemical methods were employed to characterize this film. When the film was electropolymerized on an electrode, it showed excellent catalytic activity toward the oxidation of dopamine (DA) in pH 4.0 phosphate buffer solution. In addition, the overlapped voltammetric responses of dopamine and ascorbic acid were resolved into two well-defined peaks by the film-modified electrode with a large peak separation of 0.17 V. A calibration curve for DA was obtained by the amperometric method in the range of 3.0-195.0 mu M with a correlation coefficient of 0.9997. The film-modified electrode has been successfully used to measure the concentration of DA in injections and human serum samples.