Effects of NaOH concentration in the electrolyte on the thickness of micro-arc oxidization coating on ZASi12 alloy were observed. The microstructure and phase constituent of the ceramic coating were analyzed by SEM （scanning electron microscope） and XRD（X-ray diffraction）. The results reveal that a good coating with thickness of 169 μm can be obtained in electrolyte with 2.0 g/L NaoH concentration. It is found that there exist obvious electric discharge channels in the coating with the coating and the substrate inserting into each other. The film is composed of α-Al2O3 phase and γ-Al2O3 phase.