Abstract: Al₂O₃ materials with MgO and La₂O₃ as additives were prepared by hot-pressing. The density, microstructure and phase composition of the samples were studied by the Archimedes method, SEM and XRD. The mechanical properties were studied by the three-point bending test. The dielectric properties and gas tightness were studied by the resistance meter and helium mass spectrometer leak detector. The results show that the average grain size of the sample sintered at 1500 ℃ is less than 1 μm. The bending strength of samples is more than 600 MPa. The dielectric loss is 4.00 × 10^-4 and the leak rate is 2.2×10^-9 Pa·m³·s^-1 for the sample with 2% La₂O₃.