Chemically synthesized poly(aniline-co-fluoroaniline) [poly(An-FAn)] powder were deposited on platinum substrates using thermal evaporation technique [poly(An-FAn)/vac]. These films were characterized using spectroscopic and cyclic voltammetry techniques. Electrical conductivity and molecular weight of copolymer have been measured. Results revealed that the structure of poly(An-FAn) is maintained during thermal evaporation. The response of poly(An-FAn)/vac films in terms of change in resistance with different concentration of ammonia shows its utility as a sensor material. The films show good response for ammonia. The sensing of 50 ppm of ammonia was achieved with response and recovery time of 13 and 80 seconds, respectively.