Abstract Polyaniline (PANI) and polyaniline/fly ash (PANI/FA) composites with various concentrations of fly ash (20%, 40% and 50%) were synthesized by the process of in‐situ polymerization. The samples were characterized by powder X‐ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. Moreover, the dc conductivity of the samples was measured as a function of temperature in the range 80–290 K and it was found that the addition of FA decreases the conductivity. The temperature dependence of the dc conductivity for PANI and FA/PANI composites has been explained on the basis of the quasi one‐dimensional variable hopping model. A very good agreement was found between the experimental data and the theory. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)