Zirconia coating was produced on aluminium alloy by plasma electrolytic oxidation (PEO). The alkaline electrolyte containing Zr(OH)a4 powders was used. The composition and structure of the coating were investigated by XRD, EPMA. The results show that the coating consists of a t-ZrO2, a m-ZrO2, a | /SUB>-Al2O3 and a ||/EM>-Al2O3. a t-ZrOa2 is the main phase and distributes in outer layer of the coating, however, a | /EM>-Al2O3 appears in inner layer of the coating. Many micro-particles appear on the coating surface with dimension of a 1￡2| aa. In the process of plasma electrolytic oxidation, Zr(OH)a4 powders move and deposite on the mouth of plasma discharge channel under the effect of electric field force, then it is transformed to ZrOa2 by the high temperature of plasma discharge.