The thermal properties of BaO-TiO₂-GeO₂-SiO₂ based glasses have been investigated. The temperature differences, ΔT, between the crystallization onset temperature and glass transition temperature were over 95°C. The wide range of ΔT enables the fabrication of practical fibers with a core/clad structure including partial crystallization. The rod-in-tube method was used for fabricating fiber preform, and the fiber drawing was successfully achieved. The double clad fiber with the core diameter of 6.5 μm, the 1st clad diameter of 24.5 μm, and the 2nd clad diameter of 125 μm was obtained over 100 m in length. The propagation loss of the fiber was 1.8 dB/cm. The crystallization onset temperature of the 1st cladding is lower than other glasses, so that only the 1st cladding is selectively crystallized by post-heating for active devices. Furthermore, the 1st cladding contains CuO to assist heating by absorbing the energy of laser irradiation. Fusion splicing to the conventional silica fiber was also achieved, in spite of the different thermal properties of BTGS glass and silica glass, by precisely controlling the heating power and heating position of the fiber. The splicing loss with less than 1.5 dB per point was achieved.