Metallographic observation was carried out by scanning and transmission electron microscopy to evaluate microstructural characteristics of partially austenitized and isothermally transformed 1.0C-1.5Cr bearing steel. It was observed that lower bainite formed in the local region of specimen partially austenitized and isothermally held at $250^{circ}C$ for 1/3 hr and formed in almost all area of the specimen isothermally held at $250^{circ}C$ for 2 hrs. Lower bainitic carbides with midrib was also observed in the specimen partially austenitized and isothermally held at $250^{circ}C$ for 4 hrs. Midrib was nearly carbide-free region and thicker in the vicinity of spherical carbides than the other region. Lengthening speed of lower bainitic carbides was remarkabey increased at isothermal holding time ranging from 2 hrs to 4 hrs.