Conducting composite nanofibers were fabricated from a mixture of multiwalled carbon nanotubes (MWNTs) and a polyaniline (PANi)/poly(ethylene oxide) (PEO) blend using an electrospinning process. We observed a surprising transition in the electrical conductivity of the conducting composite nanofibers while measuring the I-V characteristics of the nanofibers aligned on an electrode when they were exposed to an applied high voltage. We believe that this unexpected transition is closely related to the self-heating of the MWNTs incorporated into the conducting polymer. This type of self-heating method will be very helpful in enhancing the electrical properties of nanoscale conducting composite fibers. (C) 2008 Elsevier B.V. All rights reserved.