As an optical material, Y₂O₃ transparent ceramics are desirable for application as laser host materials. However, it is difficult to sinter and dense of Y₂O₃ hinders the preparation of high-quality optical ceramics via traditional processes. In this work, we use La₂O₃ as a sintering aid for fabricating high-transparency Y₂O₃ ceramics using a vacuum sintering process. It is demonstrated that the in-line optical transmittance of 15.0 at% La-doped Y₂O₃ at a wavelength of 1100 nm achieves a transmittance of 81.2%. A sintering kinetics analysis reveals that a grain-boundary-diffusion-controlled mechanism dominates the faster densification at high La³⁺ concentrations. It is also shown that both the mechanical and thermal properties of Y₂O₃ transparent ceramics are significantly improved upon the increase of La₂O₃ sintering additives. The results indicate that a La-doped Y₂O₃ transparent ceramic is a promising candidate for a laser host material.