Effects of sintering additives on mechanical and electrical properties of Gd-doped barium titanate ceramics have been studied by measuring their electrical resistivity, bending strength, and ESR spectra. The bulk density of the sample prepared by sintering at 1100°C with small amounts of BaB2O4 doped as sintering aids was as high as 90% of the theoretical value. Semiconducting BaTiO3 was obtained by sintering the BaB2O4-doped samples at 1100°C. The electrical resistivity of the 3mol% BaB2O4-doped sample sintered at 1100°C was the lowest in all samples and its PTCR jump was more than 4 orders of magnitude. In addition, the bending strength of the sample was the highest in all samples and the value was close to that of the sample sintered at 1380°C without sintering additives. The line width of the ESR signal of Gd3+ observed in the sample sintered at 1100°C with BaB2O4 was almost equal to that in the sample sintered at 1380°C without sintering additives. The result showed that in the samples doped with BaB2O4 as a sintering aids, Gd3+ ions were dissolved uniformly in BaTiO3 grains at a sintering temperature of 100°C.