Optical fibers possessing a crystalline oxide core have significant potential for novel and useful electro- or nonlinear-optic waveguides. Presently, however, their utility suffers from the slow speed and limited cladding materials afforded by conventional crystal-fiber-growth techniques. Described herein is the development of single phase bismuth germanium oxide crystalline core fibers using conventional glass fiber drawing. More specifically, fibers were fabricated and evaluated based on 2 embodiments of the molten core method. In a first approach, a Bi4Ge3O12 single crystal was employed as the precursor and sleeved inside a borosilicate glass cladding. In the second approach, additional Bi2O3 was included along with the Bi4Ge3O12 precursor single crystal. Glass clad fibers drawn from the precursor Bi4Ge3O12 single crystal resulted in a polycrystalline core with various crystal morphologies (line-like, dendrite-like, and uniform grains) as will be discussed, while fibers drawn from the Bi4Ge3O12 single crystal surrounded by Bi2O3 resulted in a more homogeneous microstructure. The eulytine crystal structure was crystallized using both approaches, with the formation of a secondary crystal phase using the second approach. More particularly, this work aims at showing that single phase and phase pure crystalline oxide core optical fibers can be achieved using conventional glass fiber draw processes, although further optimization is necessary for obtaining single crystalline core fibers.