In this work, cyclic voltammetry (CV) and chronoamperometry (CA) were used to study the electrodeposition mechanism of red selenium on platinum and (ITO) substrates from aqueous solution containing (SeO2) and sodium citrate as support electrolyte with pH 4.3 at ambient temperature. The potentiostatic current transients were analyzed according to Scharifker–Hills model. The morphological characterization of the deposit was carried out by Scanning Electron Microscopy (SEM), whereas the optical one was realized by UV-Visible spectroscopy. The results shown that the nucleation mechanism of Se on each substrate is instantaneous with a three-dimensional growth of the hemispherical nuclei. The nucleation density (N 0) is exponentially increased with the applied overpotential. Se thin film has an energy gap of about 2.4 eV.