Flow characteristics at Re = 660-3000 in a serpentine channel are measured. A scale-up model whose channel hydraulic diameter is 50 times as large as that for a proton exchange membrane fuel cell (PEMFC) is used for the measurements. The flow conditions correspond to operating conditions for PEMFCs of 25-40 cm(2) at current density of 1-3 A/cm(2) when the fuel utilisation ratio is 0.75 and air is used for the O-2 supply. Two different porous media are used to simulate the gas diffusion layer (GDL). The results suggest that although the leakage flow rate is rather insensitive to the total flow rate, it increases significantly depending on the increase of the GDL permeability. Increasing the flow rate or the permeability enhances the sectional secondary flows and is expected to enhance mass transfer on the GDL. It is confirmed that the flow becomes turbulent around the bend even at Re = 660. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.