The rheological behaviour of unsaturated polyester resin-organoclay (Cloisite 15A) nanocomposites at various clay contents, prepared by melt mixing was investigated. Styrene-free resin was used for high shear mixing and the elimination of the viscosity changes due to solvent evaporation. Complex viscosity-temperature curves showed a decrease in viscosity with increasing temperature followed by formation of a plateau at a particular temperature, depending on the clay content.  This behaviour is characteristics of systems with a network structure. The results of small angle X-ray diffraction and TEM analysis are in agreement with the formation of a physical network in which nanoclay particles act as the nodes while polymer chains serve as the links. It appears that at low temperature, high shear forces break the nanoclay agglomerates and/or stack more efficiently, and in so doing make more nanoparticles available against polymer chains to form a network.