Ti-Al-O-N films were synthesised by reactive unbalanced magnetron sputtering of powder metallurgically produced TiAl targets with an Al/Ti atomic ratio of 60/40 in an argon/oxygen/nitrogen atmosphere. The evolution of chemical structure, microstructure and mechanical properties was studied over a wide composition, ranging from the nitride to the oxide side. The chemical structure and microstructure was analysed using energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and X-ray diffraction (XRD). Mechanical properties were analysed using nanoindentation. The increasing oxygen partial pressure PO2 at constant nitrogen partial pressure PN2 or increasing PN2 at constant PO2 leads to the formation of a dual-phase structure consisting of fine TiAlNO crystallites with face-centered cubic lattice and an amorphous fraction consisting of Al2O3 and TiO2. Hardness and elastic modulus were found to be adjustable between 10 - 23 GPa and 150 - 320 GPa.