CaO doped nanofibrous zirconia (ZrO2) was fabricated by calcination of electrospun zirconium oxychloride (ZrOCl2)/ calcium nitrate (Ca(NO3)(2))/polyethylene oxide (PEO) composite fibers. ZrO2 nanofibers were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD). It is revealed that CaO content variation in ceramic filaments calcined at 1200 degrees C allows fabricating fully monoclinic, or fully cubic zirconia nanofibers, or nanofibers containing both tetragonal and cubic phases. CaO stabilized fully tetragonal zirconia nanofibers can be prepared at lower calcination temperature.