A series of xBaO–yB2O3–zBi2O3 (x + y + z = 100, mol%) glasses were synthesized and added to BaTiO3 ceramics as a sintering aid to reduce the sintering temperature. The thermal and dielectric properties of the glasses and glass structures were characterized. Glasses with a high △T (difference between crystallization start temperature and glass-transition temperature) were the focus of this work. Composites with 70-mass% BaTiO3 and 30-mass% glasses and composites with high relative density and excellent dielectric properties were obtained after sintering at 600 °C. Secondary phases were formed in most of the composites; three glasses with a high △T value were formed without a secondary phase at 800 °C. Raman analysis showed that the glasses with a high △T contained Bi–O–Bi and B–O–B networks, which likely influence the thermal stability of the glasses, resulting in glasses suitable for sintering aids for BaTiO3 powders.