Polypyrrole/sulfonated polyaniline (PPY/SPANI) composite films have been prepared by direct electrochemical polymerization of pyrrole in an aqueous solution of SPANI. Spectroscopic results demonstrated that the polyanion, SPANI, was incorporated into the PPY matrix as a dopant. The composite films exhibited a higher thermal stability than that of pure PPY. Scanning electron microscopic images revealed that the composite film had smooth and compact morphology. Furthermore, a simple ammonia sensing device based on the composite film showed high sensitivity and a low limit of detection. (c) 2007 Elsevier Ltd. All rights reserved.