This paper presents some results of plasma oxidizing of Al alloys. The oxidation of aluminium alloys was carried out in the mid-frequency pulsed excited plasma. The processing temperature was 450~500°Cand the processing time was 4 hours. The modified layer was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM observations indicated that there were no evident defects appeared in the modified layer. The immersion experiments in 3.5% NaCl solutions were carried out to test the effect of plasma oxidation on the corrosion resistance of Al alloys. After immersion for 200 hours, the severe pit-corrosion was occurred on the untreated sample surface while for the treated sample no evident corrosion was observed.