Applying plasma electrolytic oxidation in condition of Na₂SiO₃-NaOH solutions on pure aluminum 1070 and aluminum alloy 3003 . The thickness and microhardness of ceramic coatings were tested, and microstructure and phase composition of ceramic layer were analyzed. Results showed that, ceramic coatings of pure aluminum 1070 was consisted of phase α-Al₂O₃and phase γ-Al₂O₃, while aluminum alloy 3003 contained phase γ-Al₂O₃only; At the same processing time, the ceramic coatings of aluminum alloy 3003 were thicker but lower in micro-hardness and compactness than those of pure aluminum 1070 . Manganese element inhibited the formation of high temperature alumina phase on the reaction process.