Highly fluorescent nanofibers were prepared by electrospinning the solutions containing poly(p-phenylene vinylene) (PPV) precursor and poly(vinyl pyrrolidone), followed by thermal conversion. Different morphologies from uniform helical to ultrathin straight ones were controllably prepared by adjusting the amount of PPV precursor in electrospinning solutions. The experimental data suggest that the viscosity and conductivity of electrospinning solution and the operating voltage are the main factors that affect the formation of the helical structures. These different nanofiber morphologies may be advantageous depending on the applications. (c) 2006 American Institute of Physics.