This paper reports the preparation of bead-free ultrafine uniform nanofibers with a narrow fiber diameter distribution from fluorinated polyimide by electrospinning. Increasing the electrical conductivity of polymer solutions by the addition of salts and decreasing the discharge rate of water from the polymer by decreasing the humidity in the surrounding air decreases the diameter of the electrospun nanofiber. Ultrafine uniform nanofibers were achieved using these new salt and humidity conditions, and we successfully prepared bead-free ultrafine uniform nanofibers with a narrow range of nanoscale diameters (33 +/- 5 nm). Polymer Journal (2010) 42, 514-518; doi:10.1038/pj.2010.33; published online 28 April 2010