Water　content　in　the　membrane　and　the　presence　of　liquid　water　in　the　catalyst　layers　(CL)　and　the　gas　diffusion　layers　(GDL)　play　a　very　important　role　in　the　performance　of　a　PEM　fuel　cell.　To　study　water　transport　in　a　PEM　fuel　cell,　a　two-phase　flow　mathematical　model　is　developed.　This　model　couples　the　continuity　equation,　momentum　conservative　equation,　species　conservative　equation,　and　water　transport　equation　in　the　membrane.　The　modeling　results　of　fuel　cell　performances　agree　well　with　measured　experimental　results.　Then　this　model　is　used　to　simulate　water　transport　and　current　density　distribution　in　the　cathode　of　a　PEM　fuel　cell.　The　effects　of　operating　pressure,　cell　temperature,　and　humidification　temperatures　on　the　net　water　transfer　through　the　membrane,　liquid　water　saturation,　and　current　density　distribution　are　studied.　©　2006　Wiley　Periodicals,　Inc.