Micro-arc oxidation (MAO) method was used for the surface modification of an Mg-5wt.%Li alloy. Ceramic coatings were in-situ fabricated on the Mg-Li alloy. The morphology feature, phase composition, and corrosion-resistance of the formed ceramic coatings were studied by SEM, XRD, and electrochemical methods, respectively. The results showed that the coatings produced in a sodium silicate solution system were composed of MgO and Mg2SiO4. The ceramic coating became thicker and the content of Mg2SiO4 phase increased as the concentration of Na2SiO3 increased in the solution. The coating was loose at the low concentration of Na2SiO3 and was compact at the high concentration of Na2SiO3. The coated samples had a better corrosion resistance than the Mg-Li substrate in terms of the Tafel polarization curves and the cyclic voltammetry curves (CV).