Among conducting polymers, polyaniline has been extensively studied due to its high environmental stability, controllable electrical conductivity and interesting redox properties associated with chain nitrogen. Potential applications of polyaniline include organic lightweight batteries [1], microelectronics [2, 3], electrochromic displays [4], electromagnetic shielding [5] and sensors [6–9]. Polyaniline can be prepared by the electrochemical or chemical oxidation of aniline [10, 11]. Ammonium persulfate is generally used as the oxidizing agent for the preparation of polyaniline from aniline. The incorporation of metal in the form of nanoparticles in the polymer matrix forms composite materials, which have proved to exhibit improved performances over those of the polymer alone [12]. The preparation of gold nanoparticle–polyaniline composite material has been reported using preformed polyaniline by exploiting the multi-oxidative states of the polymer [13, 14]. Recently, it was found that chloroaurate ions (AuCl4 ) can also be applied as an oxidant for the oxidative polymerization of pyrrole [15, 16], leading to the formation of gold particles together with polypyrrole. Reports are also available regarding the oxidative polymerization of o-anisidine [17] and hexadecylaniline [18] by using chloroaurate ions as an oxidant. In the above mentioned work special emphasis was given on the structure and properties of gold nanoparticles, and little attention has been paid to the morphology and properties of the polymer simultaneously generated with the gold particles. Use of hydrogen peroxide, which acts as both oxidizing and reducing agent, has been reported to produce a gold–polyaniline composite [19] having gold particle sizes of 26 nm (as evidenced by XRD analysis). Recently, the preparation of gold–polyaniline composite material has been reported using HBF4, with gold particle sizes in the 0.8–1.0 lm size range [20]. Recently, we reported [21] a gold–polyaniline composite material in toluene solution by using a phase transfer catalyst, where polyaniline nanoballs with few microns in size become decorated by gold nanoparticles (10–50 nm). The methods reported to date tend to produce relatively large gold particles. There is, therefore, a need to develop synthetic approaches that readily enable nanosized metal particles to be obtained. In this communication, we describe a simple and in-situ route for the synthesis of polyaniline–gold thin composite film by using aniline and auric acid as the precursors. The average sizes of the resulting gold nanoparticles are 6–7 nm, which are dispersed in the polyaniline film. During the synthesis AuCl4 ) behaves as an oxidizing agent causing the conversion of aniline to polyaniline and reduction of AuCl4 ) leads to gold nanoparticles that are stabilized by the polymer matrix. Aniline was purchased form BDH (London) and distilled at a reduced pressure over zinc metal. The middle fraction was collected and stored at )10 C under argon. Methanol was obtained from Merck. HAuCl4 (Aldrich) was used to prepare a stock solution of HAuCl4 (10 )2 mol dm) in distilled water. K. Mallick (&) AE M. S. Scurrell Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, WITS 2050 Johannesburg, South Africa e-mail: kaushik.mallick@mailcity.com