The current oscillation normally seen at the beginning of the plateau of polarization curves was found to be influenced strongly by the solution viscosity. The role of viscosity for iron dissolution in sulphate solution was studied by polarization curves, ac and electrohydrodynamical impedances. It was found that the charge and mass transport processes are not changed by the viscosity. However, when the glycerol was added to electrolyte the viscosity of the solution changes. So, the hydrodynamic conditions at the electrode surface also change and consequently the oscillation processes can be eliminated.