Pb-O, La-O, Zr-O, Ti-O thin films were prepared by reactive rf-magnetron sputtering of metallic Pb, La, Zr and Ti target in an atmosphere of mixed gas of argon and oxygen. The deposition rate, crystal structure and optical properties of sputtered films were studied as a function of the partial pressure of oxygen (Po₂). Total pressure was controlled to maintain a constant value of I Pa. The deposition rate of the films decreased remarkably when the partial pressure of oxygen exceeded a certain value. Generally, with the increase of the input power, the critical Po₂ shifted to high pressure side. When films were deposited in higher Po₂ than the critical, oxide thin films were prepared. From the measurement of optical emission spectra during sputtering, the formation of oxide on the surface of target was confirmed, resulting in the decrease of the deposition rate.