Applying the technology of micro-arc oxidation to form ceramic coatings on aluminum alloy 7075 . The thickness and micro-hardness values of coatings in different concentration of sodium aluminate were tested, and morphology of surface and cross-section of coatings were observed by using scanning electron microscope ( SEM) and metallographic microscope. Results showed that, embossments like " volcanic vent " were presented on the surface of MAO coatings prepared in different sodium aluminate concentration. In addition, metallurgical bonding mode like zigzag was observed between coating and substrate, coatings were continuous and symmetrical with micro-hardness of 1080 HV0 . 1 .