Zirconia thin films were deposited by an r.f. magnetron reactive sputtering method. Three kinds of target (pure Zr metal and compounds of Y-ZrO2 and Mg-ZrO2) were employed. The phase characteristics of the three series of films deposited with various oxygen partial pressures and substrate temperatures were investigated. It is found that only monoclonic phase was formed in the sputtered thin films when using Zr target, and both tetragonal and monoclinic phases were formed when using the compound targets.