Composites of conducting polythiophene (PTh) with the host filler multi-walled carbon nanotube(MWNT) have been synthesized by the in situ gamma-radiation-induced chemical polymerization method at room temperature. The resultant cable-like morphology of the composite (PTh-MWNT) structures was characterized by field-emission-scanning electron microscopy with the energy dispersive spectroscopy, Fourier transform infrared, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. The characterizations of the molecular structure of the PTh-MWNT composites indicated that interfacial entrapment Occurred between the MWNT and PTh; and the MWNT functioned as a template for PTh polymerization. The standard four-point probe method was utilized for measuring the conductivity of the samples. The conductivity through the PTh-MWNT composites was much higher than the value obtained for the bulk PTh powders synthesized by the same method. The PTh-MWNT composites showed improved thermogravimetric stability compared to the PTh homopolymer in the temperature range 0-800 degrees C. (C) 2008 Elsevier B.V. All rights reserved.