Solid polymer electrolytes based on acrylonitrile-butadiene rubber (NBR) and LiClO4 were prepared and their conductivity was evaluated. The effect of nitrile group -CN/LiClO4 mole ratio on the conductivity was investigated. The maximum conductivity of 1.21 x 10(-4) S cm(-1) (20 degrees C) was achieved in the NBR/LiClO4 composite at the -CN/LiClO4 mole ratio of 1/2.5, which was in accordance with the strongest coordination between -CN and Li+ indicated by Fourier transform infrared spectrometry measurement. The conductivity was further increased by two to three times when 30 phr epoxy resin was introduced into NBR, and the conductivity could retain around the maximum value with the -CN/LiClO4 mole ratio ranged from 1/2.5 to 1/3.5, while the conductivity of NBR/LiClO4 composite existed a decrease in the same range. Field emission scanning electron microscopy and atomic force microscopy characterization showed that epoxy resin significantly improved the dispersion of LiClO4, leading to better surface smoothness of NBR/epoxy resin/LiClO4 composite film and contributing to the increase of ionic conductivity. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2340-2345, 2010