The electrodeposition process of selenium has been studied by voltammetry (CV) in connection with a rotating disc electrode (RDE) technique. The paper discusses the mechanism and the rate-determining step of Se deposition. It has been determined that the rate of the Se monolayer-forming process observed at ca. 0.6 V vs. NHE is diffusion controlled, not surface activation barrier-dependent. It is proposed that this process is an overpotential deposition process (OPD) and not an underpotential deposition process (UPD). The diffusion coefficient for the reacting species was determined as 2.2 x 10(-5) cm(2) s(-1). The reacting species are proposed to be identified with HSeO3- ions. The transfer coefficient, alpha, for this process was calculated as 0.3, exchange current density, j(o), as 1.1 x 10(-6) A cm(-2), and the rate constant, k, as 9.1 x 10(-7) cm s(-1), respectively. Analysis of RDE data recorded for the Se bulk deposition process taking place at ca. -0.1 V vs. NHE and fitting them with either the Levich or the Koutecky-Levich equation indicates that this process is a diffusion-dependent one. The calculated diffusion coefficient was determined as 1.1 x 10(-5) cm(2) s. These data, together with experimental condition (pH) allow one to propose H2SeO3 molecules as those being reduced during the formation of the Se bulk deposited layer. The transfer coefficient, cc, for this process was calculated as 0.1, exchange-current density, j(o), as 7.7 x 10(-6) A cm(-2), and the rate constant, k, as 1.6 x 10(-4) cm s(-1), respectively. The comparison of kinetic parameters for six-electron and four-electron processes proves that the reaction responsible for building up the Se film is six-electron reaction. (C) 2015 Elsevier B.V. All rights reserved.