Abstract: The growth mechanism of anodic films in the mixture of sulphuric and oxalic acids were studied. It was found that double peaks appeared in voltage-time transits during anodizing at constant current density in exalic acid with small addition of sulphuric acid. With increase of sulphuric acid concentration, the second peak gets closer to the first continuation period shortens. An adsorption competition mechanism was proposed to explain the effect of the amount of ox-alic concentration on the voltage-lime transits, the film growth rate, the hard-ness and abrasion resistance of the film. The mechanism can also explain the reason lor the appearance of the double peaks.