Abstract: The corrosion behavior of anodized AZ91D magnesium alloy in neutral 1%(w) NaCl aqueous solution was investigated by salt spray test, polarization curve, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and scanning electron microscope (SEM). The results showed that the corrosion behavior of Mg alloy presented characteristic changes due to anodization. For example, the unsealed anodic film could be sustained in 5% NaCl salt spray beyond 200 h, Ecorr of anodized magnesium alloy shifted up and the inductive period for pitting corrosion was obviously prolonged, and the impedance modules in high frequency of anodized alloy were several thousand times those of unanodized alloy. All these proved that anodization process made the alloy gain excellent property of anti-corrosion. The evolution of fractal dimension (Df) was first utilized to depict the corrosion process of anodized AZ91D magnesium alloy and shown as rapid increasing in the initial, fluctuating in the medium and decreasing in the last. This evolution was related with the three different corrosion stages of anodized AZ91D magnesiumalloy in 1%NaCl solution.