A method based on the melt flow index rather than the conventional zero shear viscosity is suggested to estimate the activation energy for viscous flow of polymer melts. The method is particularly attractive due to its simplicity and because all the conditions for its derivation fit rather well within the validity range of applicability of the Arrheniustype equation relating viscosity and temperature. Values of activation energy for viscous flow using the suggested technique are calculated for a number of polymers falling within the olefinic, styrenic, cellulosic, and engineering thermoplastic groups.