Exfoliated polystyrene nanocomposites have been synthesized by in situ bulk multistep polymerization of polystyrene (PS) in the presence of the filler. The filler was layered double hydroxide (LDH)-tetracalcium aluminate hydrate, modified by the intercalation of benzoate anions (Ca4Al2(OH)(12)(C6H5COO)(2)center dot xH(2)O). Benzoate anions were found to increase the interlayer distance of the original filler. At the same time, the organophilicity of the filler was increased. The LDH was prepared using a variant of the rehydration method. The PS/LDH composites were characterized by X-ray diffraction (XRD), infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), and transmission electron microscopy methods. XRD and TGA results pointed to the successful incorporation of the filler within the polymer matrix. However, XRD results indicated that a characteristic layered structure of the filler had disappeared, i.e. the delamination had occurred. The filler was dispersed within the matrix in a form of nanosized monolayer particles, i.e. a nanocomposite material was prepared.