The electrochemical behavior of HSeO3 and H2SeO3 in HNO3 has been investigated on hanging mercury drop electrode (HMDE) by the use of cyclic voltammetry. Electro-reduction of HSeO3 is chemically irreversible and gives a shoulder at positive potential side of H2SeO3 peak at +200 mV. When scan rate is increased, the peak of HSeO3 is separated from the peak of H2SeO3. The product of the first peak which appears at a more positive potential effect the reaction which may take place upon the electrode surface because this product changes the characteristic properties of it. The reduction product or products passivate HMDE surface. Therefore, formation of Se(0) is observed by chemical reaction between H2Se and Se( IV) at the passivated electrode surface. It is found that the number of reduction peaks depends on sweep rate in positive side of potential scale. The chemical reaction between Se and Hg is slower than that of the reaction between H2Se and Hg. It is also observed that HgxSey is formed at electrode surface and reduced at more positive potential than that of corresponding to the reduction of Se( IV) to H2Se. At a very low scan rate, a broad peak at around -950 mV is observed for the reduction of Se( IV) to Se(0) at the electrode passivated by selenium compounds. Number of sweeps affects the passivity of HMDE without application of deposition potential for Se( IV). (C) 2017 Elsevier Ltd. All rights reserved.