Er-doped Al2O3 films were prepared using the magnetron-sputtering method, and the films were thermal-annealed. We measured the refractive index and X-ray diffraction patterns of the films, and it was found that the films were amorphous at annealing temperatures up to 600 ℃, and the refractive index was 1.67 at 1.5 μm. We investigated the correlation between the photoluminescence intensity and Er-doping content, and the optimal deposition conditions for the films were obtained. We simulated the mode field distribution and achieved the structural parameter of the waveguide where the interaction between light and Er-doped layer is the maximum. We further optimized the fabrication conditions and achieved Er-doped Al2O3 waveguide with smooth side wall and low optical loss. The 2 μm-wide waveguide has an optical loss at 1.6 dB/cm at 1.31 μm. Compared with the alumina ridge waveguide with a loss of 3.8 dB/cm prepared by the ultrafast laser ablation method, the loss is greatly reduced, showing the potentials of the Er-doped Al2O3 waveguide used as on-chip optical amplifiers.