The influence of 30% (v/v) organic cosolvent in 1.0 mol dm(-3) HClO4 on the OER electrode kinetics, surface properties and electrode stability of IrO2-based electrodes was investigated by cyclic voltammetry and polarization curves. The Tafel coefficients in the presence of cosolvent are explained in terms of the change of the rate-determining step (r.d.s.) of the OER electrode mechanism, coating dissolution and/or cosolvent oxidation. Of the several cosolvents investigated t-BuOH and PC show less effects on the OER and electrode properties making them the best choice for organic eletrosynthesis applications, in contrast to AN, which causes coating dissolution, and DMF and DMSO which show an anticipation of the voltammetric current.