Polystyrene (PS)/organophilic montmorillonite (OMMT) day nanocomposites were prepared by a solvent casting method using chloroform as a cosolvent. Intercalation of the OMMT in the PS matrix was achieved as revealed by X-ray diffraction. The IR spectra of the products indicated that the OMMT is homogeneously dispersed in the PS matrix. A thermogravimetric analysis (TGA) showed that the onset temperature increases linearly with the clay content. The glass-transition temperature of the PS, examined using differential scanning calorimetry, had a trend similar to that from the TGA. The rheological properties of the PS/OMMIT nanocomposites were also investigated via a rotational rheometer with a parallel plate geometry, and they exhibited sharper shear thinning and increased storage and loss modulus with day content. Furthermore, the shear viscosity obtained from the steady shear experiment was well correlated with the complex viscosity obtained from the oscillatory experiment via the Cox and Merz relation. (C) 2003 Wiley Periodicals, Inc.