Serpentine flow-fields are widely used in proton exchange membrane (PEM) fuel cells due to their various advantages, including providing a proper compromise between pressure drop and water removal capability. One of the advantages of serpentine flow fields is the cross-flow under the land through the gas diffusion layer (GDL) due to the pressure difference between adjacent channels. In this study, a three-dimensional PEM fuel cell model is developed to study the cross-flow effect under the land for both across and along the land directions. Simulation results of the flow distribution along and across the channel, and the relationship between the cross-flow and the pressure difference are presented. A parametric study is conducted to investigate the effect of the GDL permeability on the cross-flow rate. The cross-flow rate increases as the permeability becomes larger because the cross-flow velocity. However, cross-flow rate reaches an asymptotic value when the permeability is greater than 10 -9 (m2) since the pressure difference between adjacent channels becomes smaller. The effect of the cross-flow on the local oxygen mass fraction is also investigated. The results show that oxygen concentrations in some locations are significantly higher due to the cross-flow under the land and secondary flows in the channel. Finally, by comparing average current densities between under the channels and the land areas, it is shown that the performance of the cell gradually decreases across the channel/land direction.