The rheological properties of poly (ether Sulfone) with different molecular weight have been measured using cone/plate rheometer. All the samples showed shear-thinning behavior and the now aCtivation energy for melts were obtained which were consistent with that reported by ICI. The correlations between zero shear viscosity (η0) and molecular weight at vareus temperatures were established and concluded that the M. of samples were close to Mc The master curve with good superposition was plotted and the two empirical constants of WLF equation were obtained and discussed.