This paper reports polythiophene/cobalt (II,III) oxide (PTh/Co3O4) nanocomposites synthesized via in situ polymerization of thiophene in the presence of Co3O4 at various molar concentrations. Samples were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and atomic force microscopy (AFM). The alternating current (ac) conductivity of the samples was studied depending on the temperature. XRD analyses indicated that the filling process decreased the pi-pi stacking distance of PT chains. The most significant shift was observed in the C-S band of PTh depending on the filling process. Thermal stability of the PTh increased with increasing concentration of Co3O4. Filling process reduced the surface roughness of PTh. The ac conductivity analyses indicated that charge transport mechanism of the samples was consistent with corraleted barrier hopping (CBH) model. The conductivity of PTh increased about 18 times for maximum filling level depending on temperature and frequency. The thermal stability and controllable ac conductivity properties of PTh/Co3O4 nanocomposites showed that they can be used in the production of micro/nano-sized electronic circuit elements with lower cost. (C) 2017 Society of Plastics Engineers