Poly(3-alkylthiophene)s represent a family of conjugated polymers that are soluble and processable, but still retaining the good electrical conductivity of the insoluble parent polymer thiophene ring backbone. Poly(3-hexylthiophene) (P3HT) is reported to be a best candidate in the family for solar cell applications. In situ polymerization of 3-hexylthiophene monomer with double-walled carbon nanotubes (DWCNTs) has been attempted with the aim of addressing two main issues, namely, the interfacial bonding and proper dispersion of the carbon nanotubes in the polymer matrix to get a high-performing polymer/nanocomposite. Fourier transform infrared spectroscopy, Raman, and X-ray diffraction studies indicate the physical wrapping of the polymer on the nanotubes in the absence of any ground-state interaction between them. The ultraviolet-visible measurements also support this view. The photoluminescence quenching indicates the effectiveness of the interface in the formation of the donor-acceptor-type composite. The impressive conductivity values encourage the utility of the composites as photovoltaic material. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2448-2454, 2010