Polystyrene/carbon nanotubes composites were readily prepared by reversed microemulsion polymerization. Compared with the composites prepared by solution mixing, the uniform dispersion of carbon nanotubes in polymer matrix could be obtained more easily and the thermal and electrical properties of the as-prepared composites were also enhanced. The as-prepared composites were deposited onto a microelectrode array to fabricate a vapor sensor. The response for different organic vapors was evaluated by monitoring the change in the resistance of the composites upon exposure to various gases. The change in resistance was of the order of about 10 3 for the composites prepared by reversed microemulsion polymerization. The chemical sensors based on the composites prepared by reversed microemulsion polymerization presented excellent reproducibility and reversibility in response. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1842-1847, 2011