Abstract: Alumina ceramics were prepared by normal pressure sintering in air, using CaO–SiO₂–TiO₂as the sintering aid. The effects of CaO content by mass in sintering aid and sintering temperature on phase composition, microstructures, and dielectric properties of Al₂O₃-based microwave ceramic samples were investigated. The results show that, the second phase of CaAl₁₂O₁₉appears in the Al₂O₃ceramics with CaO addition, and the phase content increases with the increase of CaO content in sintering aid. The dielectric constant of Al₂O₃ceramics increases with the increase of CaO content in sintering aid, while the quality factor increases first and then decreases. With the increase of sintering temperature, the relative density and quality factor of Al₂O₃ceramics increase first and then decrease, while the dielectric constant and temperature coefficient of resonance frequency keep increasing. The Al₂O₃ceramic sintered at 1450 ℃ with the CaO mass fraction of 0.4% in sintering aid presents the superior comprehensive properties, the relative density of the sintered body is 98.61%, the dielectric constant is 9.88, the quality factor is 21957 GHz, and the temperature coefficient of resonance frequency is -21.353×10^-6/℃.