Water management of polymer electrolyte fuel cell (PEFC) has been extensively studied because of its effect on the performance of a PEFC system. The transport and congelation of water significantly affect the efficiency and durability of a PEFC. Several empirical methods have been employed to visualize the spatial distribution of water in a PEFC. Experimental studies using high-resolution imaging techniques have been conducted to reveal the unknown morphological aspects that reduce the performance of a PEFC system. The X-ray imaging technique is the preferred method over other imaging techniques because of its high spatial and temporal resolution. Recently, X-ray micro computed tomography (X-ray mu CT) is introduced to better characterize the anisotropic structure of a gas diffusion layer (GDL) by reconstructing its three-dimensional structure. With the development of advanced software and hardware, the X-ray imaging technique becomes essential in the visualization of water management in PEFCs. This article reviews the X-ray imaging studies on water management in a PEFC system. (C) 2012 Elsevier B.V. All rights reserved.