ZrO2 thin films were deposited on polycrystalline alumina, glass, 〈100〉 silicon, and stainless steel substrates by metal-organic chemical vapor deposition (MOCVD). Depositions were carried out in a hot wall reactor at reduced pressure (0.6 torr) in the temperature range 400–550 °C, using zirconium cyclopentadienyl derivatives as precursors, both in a flux of oxygen and of an oxygen/water vapor mixture. High quality zirconia films with high growth rates were obtained by employing (C5H5)2Zr(CH3)2. Scanning electron microscopy (SEM) images display, in both cases, a tapered polycrystalline columnar structure of the deposits. Films grown under O2 flux show a cracked surface with a variable carbon contamination depending on the experimental conditions, while those prepared in a O2/H2O mixture are smooth and well adherent to the substrate with 5 % carbon presence according to X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction shows that samples grown in O2 flux consist of the tetragonal phase with a small amount of the monoclinic polymorph, whose percentage increases with the growth temperature. The presence of water vapor led to larger crystalline domains predominantly composed of monoclinic phase.