This work describes a characterization method for properties of nanofibers. The nanofibers were made from electrospinning poly(butylene terephthalate) solutions in hexafluoroisopropanol, with and without 5 wt% of multi-walled carbon nanotubes. The carbon nanotube-reinforced fibers showed broader distribution in diameter, rougher surface morphology, and improved thermal stability. Atomic force microscopy analysis revealed that the modulus was increased nearly three times with the addition of carbon nanotubes. (c) 2005 Elsevier Ltd. All rights reserved.