Polypropylene (PP) was melt blended with nano organo-clay masterbatch at different ratios; namely 5, 10, and 15 wt % of nano-clay. The effect of organo-clay content on the viscoelastic properties of the nano-composite was studied. A miniature laboratory mixing extruder, LME, was used to blend the nano organo-clay masterbatch with PP at 260 degrees C and 250 rpm. The blend was pelletized first, and then a thin ribbon was extruded. Two viscoelastic tests were performed; frequency sweep at constant temperature of 80 degrees C, and temperature sweep at constant frequency of 1.0 rad/s. As the loading of nano-clay increased, the storage modulus, G', and the thermal resistance increased as well. Different viscoelastic models were tried and 3-elements Maxwell model was found to describe well the viscoelastic properties of the nano-composites. The ratio of the complex modulus to the corresponding matrix modulus at different frequencies was found to vary proportional to the nanoclay loading. This dependency was described reasonably well by modified Guth model using particle aspect ratio of 12.1. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 27-36, 2011