Glass fibers with a diameter of 100-200 μm are drawn by just pulling up melts of 30BaO-15Ti O2 -55Ge O2 glass, and transparent crystallized glass fibers consisting of nonlinear optical Ba2 Ti Ge2 O8 crystals are fabricated by crystallization of glass fibers. It is clarified from linearly polarized micro-Raman scattering spectra that fibers show the surface crystallization and Ba2 Ti Ge2 O8 crystals grow from the surface to the interior, giving c -axis orientations. It is found that holes are formed frequently in the center of fully crystallized glass fibers, and transparent hollow crystallized glass fibers are fabricated through careful heat treatments, e.g., fibers with φ=200 μm show hollows (capillary-type holes) with φ=40 μm. By adding a small amount of Sb2 O3 in glass fiber preparations, transparent crystallized glass fibers with no holes are developed and second harmonic generations (SHGs) are clearly observed from such fibers. The present study proposes that transparent crystallized glass fibers showing strong SHGs would have a potential for fiber-type light control optical devices.