Mechanism of electrodeposition of zinc oxide (ZnO) thin films from aqueous solution of zinc nitrate has been studied under controlled mass transport by using a rotating disk electrode. The current associated with the electroreduction of nitrate ion has not been affected by the rotation speed due to slow electron transfer kinetics. Rate constant and transfer coefficient have been determined as 5.98 X 10(-10) cm s(-1) and 0.159, respectively, for the electrolysis in a 0.1 M Zn(NO3)(2) aqueous solution. The current, however, is increased by increasing Zn2+ concentration in the bath. The improvement of the electron transfer kinetics has been interpreted as the catalytic role of Zn2+ ion to the reduction of nitrate. The current in the presence of Zn2+ at various concentrations has been nicely described by Langmuir type adsorption of Zn2+ catalysts to the surface sites of ZnO, for which an equilibrium constant of 1.23 X 10(5) cm(3) mol(-1) (70 degreesC) has been determined. (C) 2003 Elsevier B.V. All rights reserved.