The catalyst layer is one of the key components of PEMFCs. As the electrochemical reaction occurs at the three-phase interface of the catalyst layer, it is necessary to investigate the hydrophobicity and/or hydrophilicity properties of catalyst layers, which have a large impact on the water transport and even on the performance of the PEMFC. In this paper, time dependent contact angle measurements and porosity analyses have been performed to characterize the catalyst-coated membranes. For the first time, environmental scanning electron microscopy (ESEM) has been used to measure the hydrophilicity and hydrophobicity in the catalyst layer microstructure. The micro-contact angle distribution is given based on the microstructure. It shows a micro-scale hydrophobicity and hydrophilicity study, especially for an inhomogenous material. By means of conventional time-dependent contact angle measurements, porosity measurements and micro-contact angle measurements by ESEM, the hydrophobicity and hydrophilicity of catalyst-coated membranes have been investigated. Useful information has been gained to assist the understanding of catalyst layers from catalyst-coated membranes. (C) 2005 Elsevier Ltd. All rights reserved.