A novel and simple method has been proposed for the estimation of nitrite/nitrate based on the reduction of arsenomolybdic acid to arsenomolybdenum blue using ascorbic acid. The obtained arsenomolybdenum blue complex has been oxidized by the addition of nitrite and the decrease in the absorbance of blue color is directly proportional to the nitrite quantity. The absorbance of the arsenomolybdenum blue complex has been measured at 840 nm. All the reaction variables have been optimized and Beer’s law has been obeyed in the concentration range 2–10 mg in 25 mL of aqueous phase with a molar absorptivity 4.37
104 L mol1 cm1. The relative standard deviation of the method has been found to be 1.7% for five measurements with a detection limit of 0.003 mg mL1. The method has been applied to determine nitrite/nitrate levels in biological samples as well as environmental samples.