It has been reported that a thin polybenzimidazole (PBI)/poly(tetrafluoro ethylene) (PTFE) composite membrane (thickness 25-30 mu m) can be prepared by impregnating a thin porous PTFE (thickness 15-20 mu m) in a PBI/N,N'-dimethyl actamide (DMAc) solution. In this paper, a 400 h life test of a fuel cell prepared from PBI/PTFE composite membrane was carried out at 160 degrees C with a current density i = 200 mA cm(-2). During long time test, the i-V curve and AC-impedance measurements were conducted every 12 h. The experiment data showed a 240 h period of activation. After 240 h the cell voltage started to decay. AC-impedance measurements showed internal resistance (R-s) and charge transfer resistance (R-s) decreased in the initial 240 h life test and then R-s remained almost constant and R-s increased after 240 h. The decay of fuel cell performance can be attributed to the migration of phosphoric acid out from membrane leading to the delamination between membrane and electrodes. (C) 2009 Elsevier B.V. All rights reserved.