Abstract Erbium-doped aluminum-yttrium oxide films (Er: Al2O3-Y2O3) were prepared by aerosol-UV assisted Metalorganic Chemical Vapor Deposition (MOCVD) at 410 °C and annealed at 1000 °C. The effects of humidity of carrier gas and UV-assistance on their structure and optical properties were investigated using scanning electron microscope, X-ray diffraction and Transmission electron microscopy. It was found that under low air humidity and without UV-assistance the films present a low mol% Al2O3 (10 mol%) two different structural phases are observed corresponding to the cubic and the monoclinic structures of Y2O3. When the deposition takes place under high air humidity and with UV assistance the Er:Al2O3-Y2O3 films present a very high mol% Al2O3 (88 mol%) and crystallize in the Y3Al5O12 (YAG) compound mixed with an amorphous phase. The Er3+ luminescence analyzed in the visible and IR regions, shows the classical green transitions. The best optical properties were obtained with the Er:Al2O3-Y2O3 films grown under high air humidity with UV-assistance. Under such deposition conditions, 4I13/2 lifetimes was found to be 1.1 ms. This indicates that the deposition conditions, in particular air humidity, play an important role in the luminescent properties even after annealing.