Melt extension flow is a common flow pattern during polymer processing, such as entrance converging flow in die extrusion or runner injection of polymer melts from an extruder barrel, blow molding, blowing film and melt spinning. Extensional viscosity is one of the important characterizations of the flow characteristics for polymer fluids. A new extension viscosity equation was established based on White-Metzner model, Vinogradov-Malkin viscosity equation and a new relaxation time equation in the present paper. The melt elongation viscosities of metallocene linear low-density polyethylene (mLLDPE) and polyvinyl butyral (PVB) resins at 130°C were estimated applying this viscosity equation, and the predictions were compared with the measured data of mLLDPE and PVB resins at 130°C reported from reference. The results showed that calculations were close to the experimental data. The parameters in this equation were easy to be determined and the equation was convenient to use for estimating the extension viscosity of polymer melts. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers