Al2O3 ceramics doping with Y3+ and La3+ are synthesized by conventional solid state reaction method. The structures, thermal conductivities properties and the effects of sintering temperature on the electrical properties of the samples are measured. X-ray diffraction results indicate that all the ceramics are formed to be of pure solid solution when the samples are sintered at 1500℃. Thermal conductivities of Al2O3 ceramics reach up to 8.60 W/(m· K). All the ceramics show temperature-stable dielectric characteristics. Typical dielectric relaxation behaviors are observed in Y- and La-doped Al2O3 ceramics, and the relaxation mechanism is also analyzed.