Electric resistances of Al wire electrodes immersed in various electrolyte solutions were measured during potentiodynamic polarization. An increase in resistance due to Al dissolution was observed in the negative potential range. Al dissolution occurred due to a rise in pH in the electrolyte solution near the surface under hydrogen evolution. The amount of dissolution was estimated from the change in resistance and was found to be dependent on ionic species, pH and concentration of the electrolyte solution. In an acidic solution, a cathodic current peak appeared in the j-V curve. This peak was formed by suppression of the cathodic reaction due to formation of a precipitation film of Al hydroxide covering the surface. Precipitation occurs when Al ions dissolved from the surface meet the neutral solution region formed between the alkalized solution near the surface and the acidic solution of the bulk electrolyte solution. The precipitation film of Al hydroxide is transformed to the oxide in the following potential sweep and suppresses the cathodic reaction in subsequent potential sweep cycles.