In this paper, we report a single pot synthesis of polyaniline nanoparticles and Au nanoparticle-polyaniline composite nanoparticles using vapor phase introduction of aniline monomer. The synthesis was carried out in a micellar medium using sodium dodecyl sulfate as the micelles. Also, H2O2 was used both to reduce HAuCl4 to Au nanoparticles and to polymerize aniline in the same pot. The particles were synthesized in the form of aqueous dispersion with particle sizes of about 100 nm. UV-visible absorption spectra indicated the formation of emeraldine salt form in both the PANI and the composite particles. FTIR spectra showed the formation of identical polymer in both the systems. Transmission electron microscopic investigation was carried out to measure particle sizes for both the cases. X-ray diffraction measurements showed the presence of An in the composite in addition to indicating the formation of polyaniline with low crystalline phase in both the cases. Also, the electrical conductivity of the composite nanoparticles was found to be more than 100 times than that of the polymer nanoparticles only. We also present a schematic model of the formation of nanoparticles in the micellar medium in the presence of Au nanoparticles.