A new spectrophotometric method for the determination of trace nitrite was studied. The method is based on the diazo-reaction of brilliant cresol blue with nitrite. The linear range for the determination is 0.5-12 mu g NO2-/25 mL. The detection limit is 0.5 mu g NO2-/25 mL. The method has been used for the determination of trace nitrite in water. The mechanism of the reaction was discussed.