Polypyrrole/Titanium dioxide (PPy/TiO2) composite thin films were prepared by polymerizing the monomer pyrrole in aqueous solution containing a certain amount of TiO2 particles at room temperature, and their response to ammonia (NH3) gas was examined systematically. Compared with the pristine PPy film, which reached the saturation at the concentration of NH3 beyond 200 ppm, the composite films showed more stable response and higher sensitivity. Furthermore, the PPy/TiO2 composite thin films exhibited a low detection limit of 2 ppm. The film thickness, which had a strong influence on the film sensitivity to NH3, could be controlled by varying the polymerization time. The sensitivity to NH3 gas of the samples with different content of TiO2 and different molar ratio of PPy/TiO2/oxidant was studied. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 3351-3356, 2010