Vermiculite (Verm)/polystyrene (PS) nanocomposites were prepared by dispersing a doubly organo-modified Verm (DOVerm) in PS via in situ polymerization (DOVerm/PS 1/99, 3/97, 5/95, and 7/93 mass/mass ratios). The morphology of Verm/PS nanocomposites evolved three stages as the content of DOVerm decreased in the nanocomposites: intercalation at high filler content, intermediate state of intercalation to exfoliation, and exfoliation of Verm in PS matrix with a low filler content. The morphological changes of Verm/PS nanocomposites were confirmed by the X-ray diffraction (XRD) patterns and the transmission electron microscopy (TEM) images. Compared with the pure PS, the nanocomposites filled with Verm showed significant enhancements on thermal stability and dynamic mechanical properties. Interestingly, the nanocomposites filled with 1 and 7 mass% of DOVerm exhibited more pronounced effects of Verm on the properties. It was proved that the double organo-modification clearly enhanced the ultimate properties of the Verm/PS nanocomposites. (C) 2013 Elsevier B.V. All rights reserved.