The influence of water activity on the mechanism and kinetics of Bi(III) ions electroreduction at dropping mercury electrode in chlorates (VII) using voltammetric and impedance methods was examined. The kinetic parameters determined in the examined solutions were correlated with water activity. The values of transfer coefficients, standard rate constants and activation energy point at the slight influence of supporting electrolyte concentration on the kinetics of Bi(III) electroreduction in 1-3 mol dm(-3) chlorates (VII). In the concentration range of 4-8 mol dm(-3) the values of transfer coefficients and standard rate constants increase considerably, whereas the values of activation energy decrease what testifies to the increase of reversibility of Bi(III) ions electroreduction. The character of the rate constants changes in the function of potential points at multi-stage process of Bi(III) ions electroreduction as well as a different mechanism of Bi(III) electroreduction in the solutions with low water activity in comparison with the solutions with high water activity. (C) 2010 Elsevier Ltd. All rights reserved.