Amorphous aluminium oxide thin films were deposited by reactive direct current circular magnetron sputtering. The deposition process was controlled by target voltage while the target power was adjusted to a preset value by oxygen gas flow rate. This technique allows the control over the film stoichiometry and reduces the target poisoning. A pulsed power supply was used to minimise the arcing. Oxygen was injected in the vicinity of the substrate to improve the oxidation of aluminium. The thin film properties were studied in terms of the process parameters such as target voltage, sputtering gas pressure and substrate bias voltage. The film properties studied in detail were the nanohardness, elastic modulus, film roughness, crystallographic structure, intrinsic stress, O/Al ratio, density and surface defects caused by arcing. Depending on the process parameters used, amorphous aluminium oxide thin films deposited on different substrates had nanohardness between 12.6 and 20.6 GPa, elastic modulus between 177 and 219 GPa, residual stress between - 249 and 242 MPa, O/ Al ratios between 1.30 and 1.72, and density between 2.32 and 3.77 g/cm(3). The roughness of the aluminium oxide thin film on Si was between 0.72 and 2.64 nm.