In a proton exchange membrane fuel cell (PEMFC), gas diffusion layers (GDLs) play a major role in the overall system performances. This is the reason why many research investigations try to model and optimize the GDL physical properties. Currently, the major drawback of these models is to obtain representative GDL mechanical and physical input parameters under different excitations and, particularly, under dynamic excitations. In this paper, an experimental method using a dynamic mechanical analysis (DMA) is detailed to properly obtain the GDL Young's modulus in compression (or compression modulus) for high compressive loads under dynamic excitation. As an example, a very stiff GDL is characterized and analyzed. Only the first mechanical compression is considered. The GDL compression modulus is clearly nonlinear versus the compressive loads. The dynamic load amplitude has a strong effect on the GDL hysteretic behavior. However, the frequency value of the dynamic excitation seems to have no effect on the GDL compression modulus.