Polyaniline nanocomposite was prepared in aqueous and aqueous/non-aqueous media by polymerization of aniline using ammonium peroxy disulfate as an oxidant in the peresence of hydroxypropylcellulose. The product was characterized in terms of morphology, particle size, and chemical structure. The results indicated that small and spherical nanoparticles can be obtained by using HPC in aqueous/non-aqueus media. The chemical structure of the products was studied by fourier transform infrared spectroscopy.