Compared to conventional proton exchange membrane (PEM) fuel cell with thick membrane electrode assembly, today's automotive PEM fuel cell adopts thin MEA with thin catalyst coated membrane (CCM). The objective of this modeling study is to shed light on PEM fuel cell with thin MEA under low humidity operation condition. The effects of cathode catalyst oxygen reduction reaction activity and local O-2 transport resistance on automotive PEM fuel cell high current operation are elucidated. The local O-2 transport resistance is found to have large impacts on limiting current density. The effects of cathode humidifier elimination, operating pressure, and stoichiometry ratio on PEM fuel cell performance are also discussed. The thin membrane in thin MEA has much lower ohmic resistance compared with thick membrane, and it is easy to be hydrated under low humidity condition. But H-2 crossover is stronger for thin membrane and needs to be watched out when thinning the membrane. In addition, a 50 cm(2) PEM fuel cell with counter-cross flow field is simulated for demonstration of medium scale PEM fuel cell modeling. Under 0.65 V and 50%4% humidity operating conditions, the 50 cm2 PEM fuel cell is predicted to supply average current density of 2.51 A/cm(2).