In situ one-step chemical synthesis route for the preparation of a gold-polyaniline composite in nanopores of polycarbonate (PC) membrane is reported. PC membrane, which was placed in a specially designed two-compartment cell, separated the aqueous solution of aniline from HAuCl(4) solution. Concentration gradient across the membrane caused movement of AuCl(4) (-) and anilinium ions in the pores of polycarbonate membrane. Nanopores in PC membrane acted as reaction vessels where aniline and HAuCl(4) were allowed to mix together, and the redox reaction between aniline and HAuCl(4) led to the formation of gold-polyaniline composite. The gold-polyaniline composite in PC membrane was characterised by EDXRF, XRD, UV-Vis spectroscopy, FTIR and TEM. Peak broadening in XRD suggests that Au particles formed in the membrane are nanocrystallites and average crystallite size is (24 +/- A 4) nm. TEM studies show that gold nanoparticles are randomly dispersed in polyaniline clusters formed in the nanopores of PC membrane. Characterisation results show that the surfaces of the PC membrane exposed to HAuCl(4) and aniline have significantly higher concentrations of Au nanoparticles and polyaniline, respectively.