Though Mg-alloy can be used as a new generation of implant materials with good bio-compatibility and biodegradability, its corrosion rate should be reduced to an acceptable level for the application. For that, at the present, the most commonly measure is to apply a micro-arc oxidation coating on the alloy. However, the porosity of the micro-arc oxidation coating is too large, thereby corrosive species can easy migrate inward through the micro-pores, thus degrade its protective effect. Recently, some scholars have found that pretreatment of the metal matrix can increase the density of the micro-arc oxidation coating. So in this study, Mg-alloy was pretreated by ultrasonic rolling before the micro-arc oxidation. Then the prepared micro-arc oxide ceramic coatings on Mg-alloy with or without ultrasonic rolling treatment were comparatively assessed by means of OM, SEM, EDS, XRD, electrochemical workstation (simulated humoral PBS), to reveal the effect of ultrasonic rolling treatment on the properties of micro-arc oxide ceramic coating. Results show that: after ultrasonic rolling treatment, the treated Mg-alloy matrix presents lower surface roughness, finer grains and higher hardness. In comparison with the Micro-arc oxidation ceramic coating on the un-treated Mg-alloy, the element content of Si, P and Ca is increased in the coating on the pre-treated ones, correspondingly the surface was denser and smoother, and the number of macropores significantly decreased, namely, the surface porosity reduced from 31.7% to 19.1%. From electrochemical tests we can see that, the free corrosion potential was 107 mV higher, the corrosion current density was an order of magnitude lower, and the impedance is much higher for the micro-arc oxidation ceramic coating on Mg-alloy pre-treated by ultrasonic rolling. In conclusion, the pre-ultrasonic rolling treatment could effectively improve the corrosion resistance in PBS solution of the micro-arc oxidation ceramic coatings on Mg-alloy.