A series of polymer-clay nanocomposite (PCN) materials that consist of poly(N-vinylcarbazole) (PNVC) and layered montmorillonite (MMT) clay are prepared by effectively dispersing the inorganic nanolayers of MMT in an organic PNVC matrix via in situ photoinitiated polymerization with triarylsulfonium salt as the initiator. Organic NVC monomers are first intercalated into the interlayer regions of the organophilic clay hosts, followed by one-step UV-radiation polymerization. The as-synthesized PCN materials are typically characterized by Fourier transform IR spectroscopy, wide-angle X-ray diffraction, and transmission electron microscopy. The molecular weights of PNVCs extracted from the PCN materials and the bulk PNVC are determined by gel permeation chromatography analysis with tetrahydrofuran as the eluant. The morphological image of the synthesized materials is observed by an optical polarizing microscope. The effects of the material composition on the optical properties and thermal stability of PNVCs and a series of PCN materials (solution and fine powder) are also studied by UV-visible absorption spectra measurements, thermogravimetric analysis, and differential scanning calorimetry, respectively. (C) 2003 Wiley Periodicals, Inc.