Polypyrrole-Polymethylmethacrylate (PMMA + PPy) composite films were prepared electrochemically by means of codeposition at constant potential. The films were characterized by using Infrared spectroscopy, wide-angle X-ray diffraction analysis, and scanning electron microscopy. The appearance of standard and some new absorption bands for PPy and PMMA confirms the composite formation. The mechanical properties of the conducting PMMA+ PPy films were studied and found to be improved with respect to the control PPy films. The electrical conductivity of the PMMA + PPy film was measured by using standard four- and two-probe methods. The conductivity of the films was found to depend on the pyrrole content. These conducting composites were further used as gas sensors by observing the change in the current when exposed to ammonia gas. The film gives a fast and reproducible response towards ammonia gas. (C) 2003 Wiley Periodicals, Inc.