Measurements of capillary pressure-saturation relationships under defined levels of compression for gas diffusion layers (GDL) of polymer electrolyte membrane fuel cells as thin, mixed-wettable porous media have been carried out in a newly constructed device. This article lines out the construction principle of the cell and the preconditioning procedure of the sample to measure the capillary pressure-saturation relationships under well-defined conditions and loads of compression. Three commercial GDLs (Freudenberg H2315T10A, H2315T10AC1, and SGL Carbon BA24) have been examined and a compression-depending hysteresis of the capillary pressure-saturation relationship has been measured and identified.