Single-crystal fiber (SCF) is a kind of fibrous functional crystalline material with “quasi one-dimensional” structure, exhibiting great application prospects in the fields of high-energy lasers, high-temperature sensing, radiation detection, information communication and other areas of national defense and national livelihood. In this work, ultrafine Al2O3 and YAG single-crystal fibers with the diameter from 60 μm to 100 μm and length-to-diameter ratio greater than 6 000∶1 were grown by laser heated pedestal growth (LHPG) technique. The diameter fluctuation of the obtained SCF is less than 4%, demonstrating excellent flexibility and waveguide characteristics. This work presents feasible approach for the miniaturization of SCF devices method.