A method for electrolytically etching an aluminium foil for use as an electrode of an aluminium electrolytic capacitor is described. In the method, an aluminium foil is electrolytically etched an on the surfaces thereof in a 3 to 25% hydrochloric acid solution containing aluminium chloride by application of an AC current. The AC current has a waveform, each cycle of which consists of positive and negative half cycles and an OFF time interval between the respective half cycles at which the AC current becomes zero whereby the size of pits formed by the etching is suitably controlled.