Composite nanofibers of Poly(butylene terephthalate) (PBT)/multiwalled-carbon nanotubes (MWCNTs) were prepared by electrospinning technique in the form of a random fibers web. The effect of MWCNTs on the morphology, crystallinity, and mechanical properties of the electrospun composite nanofibers was investigated by SEM, DSC, and tensile testing, respectively. SEM observations indicated that the presence of MWCNTs resulted in finer nanofibers for lower loading; however, a broader diameter was found for nanofibers with higher amounts of carbon nanotubes. It was also observed that the melt-crystallization temperature (Tc) of PBT nanofibers shifted to a higher temperature (about 8 degrees C) by the incorporation of MWCNTs which might be due to the nucleating effect of the nanotubes. The mechanical properties (specific strength and modulus) of the PBT nanofibers were significantly enhanced by the incorporation of MWCNTs.