The aim of this work is the study of viscosity influence on the diffusion of Ferrocene/ferrocenium, Ferrocenyl methyl aniline/ferrocenium and N-(ferrocenyl methyl)-2-nitro aniline/ferrocenium couples within solutions contain aqueous ethanol at different percentages as the solvent and potassium chloride as the supporting electrolyte. The dynamic viscosity of prepared solutions was calculated using the most adequate models of Faulkenhagen and of Teja-Rice. The electrochemical behavior and diffusion coefficients are investigated using two voltammetry techniques: cyclic and rotating disc...