Zirconia thin films were deposited on different substrates by reactive r.f, magnetron sputtering. It was found that zirconia layers grew preferentially in the (200) direction with a columnar microstructure that is independent of the oxygen flow, argon to oxygen flow ratios and sputtering pressure. On the other hand the substrate roughness clearly affects the orientation of zirconia. Distinct changes were observed in the case of heated substrates. The heating of the substrates does not change the form of the zirconia, but strongly influences its orientation. When the substrate temperature increases, the crystallographic orientation gets more and more random, typically for the polycrystalline state. A decrease in the optical transmittance and an increase in the colour intensity of the layers with an increase in the substrate temperature was also found. As is shown, the oxygen non-stoichiometry of the zirconia is responsible for these changes.