A flow injection catalytic method is proposed for determination of trace vanadium based on its catalytic action on a new indicator reaction between Victoria blue B (VBB) and potassium bromate in the presence of citric acid as an activator and in dilute sulfuric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of VBB injected at the maximum absorption wavelength of 618 nm. The detection limit is 0.5 ng ml−1and is independent of the initial valence state of vanadium. The relative standard deviation is 1.5% obtained from 11 standard solutions each containing 40 ng ml−1of vanadium. The sampling rate is about 15 samples per hour. This method is very simple and has been applied to the determination of trace vanadium in some natural waters with recoveries of 93-103%.