in situ polymerization of aniline was carried out in the presence of fly ash (FA) to synthesize polyaniline/fly ash (PANI/FA) composites. The PANI/FA composites have been synthesized with various compositions (15, 20, 30 and 40 wt%) of FA in PANI. The composites, thus synthesized have been characterized by infrared spectroscopy and X-ray diffraction. The morphology of these samples was studied by scanning electron microscopy. Further the a.c. conductivity of these composites have been investigated in the frequency range 102–106 Hz. The presence of polarons and bipolarons are made responsible for frequency dependence of a.c. conductivity in these composites. The Cole–Cole plots indicate clear shift in the distribution of relaxation times as the wt% of FA in PANI changes. These composites show almost symmetric semicircles of Cole–Cole plots indicating the Debye-type relaxation in their polarization response.