A method for the improvement of the signal-to-noise ratio in square-wave (SW) voltammetry is proposed. It is based on the modification of a square-wave waveform. This method is applied to cathodic stripping voltammetric (CSV) determination of selenium(IV) in nitric acid solutions. Hanging mercury drop electrode (HMDE) was used in the presence of Cu(II) ions. The optimal conditions were chosen: square-wave waveform mode. pH. time and potential of electrodeposition. Kinetic processes of copper selenide reduction with the use of SWCSV, applying different square-wave waveforms, are studied. Quasi-reversible processes are observed. The standard reaction rate constants are evaluated for different square-wave waveforms. It is shown that the determination of Se(IV) by this modified SWCSV technique is possible with an excellent sensitivity (the detection limit 8 x 10 (12) mol L (1) only for 5 min of electrode position) and good reproducibility (S-r < 8%) in a wide range of concentration (1 x 10 (11) - 1 x 10 (6) mol L (1)) of Se(IV). The presence of Mo(VI), Pb(II), Ni(II), Zn(II), Cr(VI) metal ions with molar excess around 1000 do not prevent the detection of Se(IV) signals.