Polymer nanotubes have been successfully electrospun via a single capillary spinneret instead of coaxial electrospinning. By altering the volume of ethanol under a fixed amount of poly(vinyl pyrrolidone) (PVP) and tetraethyl orthosilicate (TEOS) in the precursor, the nanotubes could be controllably produced for a proper concentration of PVP solution. Further investigation showed that the diameters of nanotubes, the thicknesses of nanotube walls, and the ratios of the thickness of the nanotube wall to the nanotube diameter (RTNWND) could be controlled by altering the amount of TEOS in the precursor. With increasing the ratios of TEOS to PVP solution, the nanotube diameters were increased and the nanotube walls were decreased. Thus, the RTNWND were decreased. The applied voltages also have an effect on the nanotube diameter and the thickness of the nanotube wall, but little on the RTNWND. The effects of ethanol and TEOS on evaporation and phase separation processes were discussed.