New organic-inorganic hybrid fibers (polyvinyl alcohol (PVA)/HfO2) were prepared by an electrospinning method using DI water as a solvent. The HfO2-acetate nanoparticles could he loaded up to 80% by weight in PVA polymer to fabricate uniform PVA/HfO2 electrospun hybrid fibers. After annealing at 140 degrees C for 12 h, electrospun PVA/HfO2 fibers were stable when soaked in water. Calcination of these hybrid fibers at temperatures ranging from 450 to 700 degrees C resulted in the formation of pure inorganic HfO2 fibers with diameters ranging from 0.1 to 0.8 mu m depending on the concentration of HfO2-acetate nanoparticles in the spinning dope. Fourier transform infrared spectroscopy and Raman spectroscopy techniques were used to investigate the crystal structures of the HfO2 fibers, which were confirmed by X-ray diffraction (XRD) results. XRD results showed the presence of both monoclinic and tetragonal crystal structures in the HfO2 fibers. The type and size of the crystals formed depended on the concentration of HfO2-acetate nanoparticles in the initial spinning dope and on the calcination temperature. In particular, the formation of stable tetragonal crystal structures in the as-spun hybrid fibers with lower concentration of HfO2 was achieved at lower temperature than the monoclinic-to-tetragonal transition temperature.