Crystallization behavior was studied in the three series of glasses: (a) (35-x)BaO·xYO_1.5·65SiO₂, (b) 35BaO·xYO_1.5·(65-x)SiO₂ and (c) (25+x)BaO·10YO_1.5·(65-x)SiO₂, with differential thermal analysis (DTA), X-ray diffraction and scanning electron microscopy. Barium silicates with spherulitic structure were main crystals precipitated from these glasses. By comparing DTA curves of powder samples with those of piece samples, it was found that yttrium oxide reduces internal crystallization in the bulk. Stability of glass against heating was evaluated with the interval between the glass transition temperature and the onset temperature for crystallization. Activation energies for crystal growth were determined by the modified Kissinger plot. It was found that YO_1.5 increases the stability of glass by increasing the activation energy for crystal growth and this was considered to indicate that YO_1.5 strengthens the glass network. In 35BaO·xYO_1.5·(65-x)SiO₂ series, however, the stability of glass decreased sharply when x exceeded 12mol%, corresponding to the anomalous property change with composition referred to in the previous study.