A highly sensitive method has been developed for the determination of trace As(III) by a square wave cathodic stripping voltammetry employing in situ plated bismuth-film on edge-plane graphite substrate as working electrode. The presence of As(III) enhanced a cathodic peak corresponding to the catalytic hydrogen wave due to Se(IV) at about -1150 mV. Linear calibration curves for As(III) determination were obtained over the concentration ranges of 0.01-1.0 microg L(-1) and 1.0-12.0 microg L(-1) at deposition times of 30 s and 10 s, respectively. The detection limit (3sigma) was estimated to be as low as 0.7 ng L(-1) As(III) at 30 s deposition time. The optimum experimental parameters and probable interference from foreign ions and organic compounds were investigated. This proposed method could be applied to analyses of certified reference material, synthetic and natural water samples.