The reaction mechanism for the reduction of Cu(II)-oxine complexes on mercury electrodes is studied by cyclic voltammetry (CV) and square wave voltammetry (SWV). The quasi-reversible two-electron transfer is analysed from a theoretical point of view according to the EED and EDE mechanistic schemes based on an analysis of the Butler-Volmer formalism. The effects of SW parameters and solution composition are analysed. Fitting experimental data with theoretical curves allowed the evaluation of charge transfer rate constants, as well as discrimination between adsorbed or soluble species. In buffered solution at pH 7.7, a k(s) value of 0.8 s(-1) was determined, for a one-step process involving adsorbed reactants and soluble products. In unbuffered solutions, a split in the redox wave is observed with k(s) values of 60 and 4 s(-1) for each process, assigned to the reduction of CuOx(+) and Cu(Ox)(2), respectively.