In the development of more efficient and stable polymer electrolyte fuel cell (PEFC), it is important to propose the optimal component shape that can generate high power and uniform the current density distribution in a single cell. In this study, our past model was improved, and simplified two-dimensional PEFC analysis model including flow and heat transfer of cooling water was made. And PEFC internal phenomenon, that is hardly measured experimentally, could be examined by using this model. The influence of changing the thickness of membrane and gas diffusion layer (GDL) on the cell performance was calculated. As a result, it was confirmed that it is possible to improve the cell output by thinning the GDL more than the membrane in case of low voltage and by thinning the membrane more than the GDL in case of high voltage, but thinning the membrane and the gas diffusion layer increased the current density distribution. In addition, by arranging the values of average current density and the current density distribution, the evaluation graphs were made, which became a help of the shape design in the membrane and the gas diffusion layer. (c) 2005 Elsevier B.V. All rights reserved.