The electrochemical oxidation reaction of nitrogen dioxide (NO2) using boron doped diamond (BDD) electrodes is presented. Cyclic voltammetry of NO2 in a 0.1?M KClO4 solution exhibits oxidation peaks at +1.1?V and +1.5?V (vs. Ag/AgCl) which are attributable to oxidation of HONO and NO2−, respectively. Moreover, the pH and scan rate dependences were investigated to study the oxidation mechanism. A linear calibration curve was observed in the concentration range of ∼1 to 5?mM (R2=0.99) with a detection limit of 11.1 ppb (S/B=3) for HONO and 58.6 ppb (S/B=3) for NO2−. In addition, the analytical performance was compared with those using glassy carbon, platinum and stainless steel as the working electrode.