To understand the deformation of biaxially stretched polytetrafluoroethylene (PTFE) membrane during the tenter frame transverse stretching process, a finite element analysis (FEA) model was established to study the stress and displacement distribution during the transverse stretching. The morphology, pore size, and mechanical properties of the membrane were also characterized. It has been found from the experimental and FEA simulation results that the tentering transverse stretching of PTFE membrane is a nonuniform stretching, the stress and displacement distribution of the PTFE membrane during tentering is nonuniform because of the nonuniform deformation and the ease of yield and plastic deformation originated from the specific structure of the virgin PTFE particles. The nonuniform thickness and pore size distribution across the membrane width resulted from this nonuniform deformation was also characterized and discussed. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116:1124-1130,2010