A highly sensitive spectrophotometric method has been developed for the determination of nitrogen dioxide (nitrite as NOz−) by reacting manganese dioxide in 1:20 perchloric acid. An amount of manganese dioxide (MnOz) equivalent to the concentration of nitrogen dioxide becomes soluble due to the reduction of Mn (IV) to Mn (II) by nitrite in acidic medium. The soluble Mn (II) ion is filtered to remove excess of MnO2and is oxidized to permanganate ion by periodic acid in presence of phosphoric acid. The violet colored solution shows maximum absorbance at 525 nm. The sensitivity of the method is 0.08 ppm based on 0.0044 absorbance, and Beer's law is obeyed in the concentration range of 0.2 to 10.0 μg/mL of NO2−. Molar absorbance is found to be 2442 at 525 nm.