The ultrafine composite fibers had been successfully achieved by electrospinning of chloroform solutions of octadecyl chitosan (O-CS) and poly(ethylene oxide) (PEO). The ultrafine composite fibers membranes were subjected to detailed analysis by Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and water contact angle (WCA). The FTIR results confirmed that ultrafine composite fibers contained the two polymers. The SEM images showed that the morphology and diameter of the composite fibers were mainly affected by the weight ratio of O-CS/PEO, the electric field strength, and the collection distance. The WCA data demonstrated that the composite fibers membranes performed a quite hydrophobic character. The special morphology of neck and porous structure was observed experimentally during electrospinning. The neck structure was due to the fibers elongated in the direction of stretching through the electric field, and the porous structure was decided by the competition between the phase separation and the fast evaporation rate of chloroform. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2113-2120, 2010