In the present manuscript, humidity sensing properties of a copolymer, poly(aniline-co-fluoroaniline) have been reported. The copolymer was prepared on indium-tin-oxide coated glass plates as well as platinum surface in the form of films using electrochemical technique (versus standard calomel electrode) in acidic medium. Synthesis of copolymer films was supported by Fourier transform infra-red, ultraviolet-visible, scanning electron microscope and cyclic voltammetry techniques. Molecular weight and electrical conductivity of these films were measured at different temperature. Polyaniline and poly(2-fluoroaniline) films were also synthesized using the same technique to compare the data with copolymer film. On exposure to humid atmosphere, the response behaviour of copolymer film exhibited a change in resistance with respect to relative humidity (RH). This copolymer film was found to be most sensitive in the 30-65% RH range and shows a linear behaviour with in this range. (C) 2008 Elsevier B.V. All rights reserved.