In the present investigation we have developed ammonia sensor using polyaniline film doped with poly (vinyl sulphonic acid). We have synthesized polyaniline by oxidative polymerization of aniline using ammonium peroxydisulfate on poly(methyl methacrylate) substrate in the presence of poly (vinyl sulphonic acid) for the development of ammonia sensor. The synthesized Polyaniline films were characterized by using UV-visible, FTIR, SEM and the electrical conductivity. The ammonia sensing behaviour of the synthesized film was studied by indigenously developed computer controlled gas chamber. The synthesized PANI film shows excellent sensing behavior for 50, 100 and 250 ppm of ammonia.