A new method to distinguish between sodium chlorite and sodium hypochlorite by ion-chromatography is described. Under the operating condition (TSK-gel DEAE-5PW glass column 8.0 mm ID x 7.5 cm with an aqueous solution containing 20 mM sodium carbonate, 10 mM sodium hydroxide and 4 mM ethylenediamine) and electrochemical detector (Toso EC-8000, -200 mV, Ag-electrode), chlorite and hypochlorite anions were clearly separated and detected and the retention times (tR) were 6.0 and 4.6 min, respectively.