Highly conducting nanocomposite film of polyaniline (Pani) with graphene (GN) was prepared by incorporating GN nanoplatelets in Pani matrix, followed by sulfonating it with fuming sulfuric acid. Sheet-like GN nanoplatelets were distributed uniformly in a Pani matrix, leading to high electrical conductivity due to π-π interaction between sulfonated Pani (s-Pani) and GN. Studies of the thermoelectrical behavior and ammonia-sensing behavior on GN@s-Pani showed high DC electrical conductivity retention under ageing conditions as well as excellent reproducible sensing response towards ammonia vapor in contrast to acid-protonated Pani.