Abstract: It was found that barrier anodic film can be formed on aluminium in (NH₄)₂MoS₄ aqueous solution. Ultramicrotomed sectioning allied with analytical TEM and ion implantation of xenon marker techniques were employed to investigate the morphology, chemical composition of the film and to measure the ion migration during anodizing. Species characterizing the electrolyte (Mo) was not detected in the film section with EDAX analysis. It was found that film growth proceeds at both the alumium/film and the film/electrolyte interfaces. The apparent migration ratio of aluminium ions is 0.44 when the anodizing current density is 1.0mA/cm².