Polyurethane (PU) nanocomposites were prepared from hectorite (HEC) and laponite without adding any organic modifier. PU-montmorillonite nanocomposites were prepared for comparison. The structure of the composites were investigated by transmission electron microscopy, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. Thermal gravimetric analysis and dynamic mechanic analysis were used for determination of the thermal and viscoelastic behaviors, respectively. Tensile tests were conducted for characterization of the mechanical properties. The results showed a 113.5% increase in the tensile strength of PU containing 7 wt % HEC compared to that of neat PU. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 832-837, 2010