The ceramic coatings on Zr-4 alloy were prepared by micro-arc oxidation in phosphate electrolyte system and silicate electrolyte system respectively. The microstructure, the phase composition and the wear resistance of the ceramic coatings in different electrolyte systems were compared. The results indicate that for the ceramic coating prepared in the phosphate electrolyte, it has thicker dense layers, about 2/3 of the whole layers, than that prepared in the silicate electrolyte; its surface micro-morphology shows typically volcano-shape character, rougher than that prepared in the silicate, but the hole is fewer, and the inner layer is compacter. The ceramic coatings in both electrolyte systems are mainly composed of t-ZrO2 and m-ZrO2, but the mass fraction of m-ZrO2 is higher in phosphate electrolyte and there may be a few zirconium silicate in the outside of the coating in the silicate electrolyte. After the micro-arc oxidation treatment, the wear-resistance of zirconium alloy has a large increase and the wear-resistance of the coating prepared in the phosphate electrolyte is superior to that prepared in the silicate electrolyte