The Scanning Electron Microscope and X-ray diffraction apparatus are used to observe the morphology character and phase composition of ceramic coating deposited on AZ31B magnesium alloy using microplasma oxidation process. The results show that the ceramic coating obtained under the condition of DC impulse source is more compact than that of AC impulse source. The ceramic coating is mainly consisted of MgSiO_3 and MgO phases. Corrosion test shows that DC impulse source is more effective than AC source to im...