Thin films of zirconia have been deposited at 733 K and below by microwave post-discharge-assisted oxidation of ZrCl4 in O-2-H-2-Ar mixtures, leading to monoclinic layers with a columnar morphology. The highest deposition rates were obtained when both H-2 and O-2 passed through the discharge, with a flowrate ratio of H-2/O-2 = 2. The results have been compared with those for a conventional chemical vapour deposition (CVD) process based on the hydrolysis of ZrCl4. Together with information gained on the post-discharge process using other investigation methods, such as mass spectrometry and measurements of atomic oxygen concentrations by NO titration, they have helped to shed light on the reaction paths. The mechanism leading to zirconia formation has been identified as being a simple hydrolysis reaction in the late post-discharge. The microwave post-discharge-assisted O-2-H-2-Ar process thus seems to behave like a conventional CVD technique in the temperature range from 573 to 733 K.