In this paper, ammonia sensor operating at room temperature based on diphenylamine conjugated polymer has been designed and developed. The structure of the polymer was established by UV-Visible, FT-IR and NMR characterization techniques. The polymer was doped with silver nanoparticles by ex-situ method in 0.6 wt%, 1.2wt% and 1.8wt% to form silver nano-composites. The thin films of the polymer and its composites were cast by spin coating on the glass plate. The response of the polymer and its composite with silver nanoparticles has been studied for gas sensor applications. The polymer showed selectivity towards ammonia gas, whereas the polymer composite with silver nanoparticles exhibited selectivity towards ammonia gas and also to ethanol vapors. The response towards ammonia gas was found to increase with the increase in loading of silver nanoparticles. Reproducibility of the polymer and its composite is studied and is found to improve with the loading of silver nanoparticles.