We have investigated the volatile organic compounds (VOCs) gas sensing properties of high conducting polypyrrole thin films prepared by plasma polymerization and doped with 4-ethlbenzenesulfonic acid (EBSA). Upon exposure to VOCs gas, the resistance of EBSA-doped plasma polymerized polypyrrole (PPPy) films decreases. The films exhibit higher sensitivities to polar analytes such as formaldehyde and acetaldehyde, but show little response to toluene and benzene. Moreover, the EBSA-doped PPPy films are hardly affected by humidity. (c) 2005 Elsevier B.V. All rights reserved.