The effect of oil dissolution by electrolyzed acidic solution was confirmed. As a result of that, the electrolyzed acidic solution obtained by electrolysis with a dilute sodium chloride and sodium sulfate solution was found to dissolve oil remarkably well, but while an ordinary acidic solution which was arranged to have the same pH as the electrolyzed acidic water hardly dissolved oil at all. The oil dissolution was assumed to be caused by the high concentration of dissolved oxygen contained in the electrolyzed acidic water. The electrolyzed acidic water of the sodium chloride solution thus decomposes a part of the oil. It was aiso recognized to have other effects, such as hydrophilicity and to produces several kinds of volatile byproducts. Since the electrolyzed acidic water of sodium sulfate did not show this kind of phenomenon, the oil decomposition was suspected to be caused by hypochlorous acid occurring at anode electrode during the electrolysis of the sodium chloride solution.