Water　management　is　one　issue　that　must　be　surpassed　to　ensure　high　membrane　proton　conductivity　and　adequate　reactant　transport　in　the　membrane-electrode　assembly　(MEA)　simultaneously.　A　well-designed　water　management　system　is　based　on　a　comprehensive　understanding　of　water　transport　in　the　inner　part　of　the　polymer　electrolyte　membrane　(PEM)　fuel　cell.　In　this　work,　the　water　transport　phenomena　in　the　MEA　PEM　fuel　cell　are　analyzed　by　using　a　mathematical　model.　The　transport　of　diluted　species　interface　is　used　to　model　the　transport　of　water　in　the　ionomer　phase　in　the　catalytic　layer　and　the　membrane　domains.　The　molecular　flux　of　water　is　defined　using　Nernst-Planck　equations,　including　migration　and　Fickian　diffusion　using　parameters　obtained　experimentally　for　diffusivity　and　mobility　based　on　water　drag　for　a　fully　humidified　membrane.　The　proposed　model　1D　model　includes　anode　gas　channel,　cathode　gas　channel,　anode　gas　diffusion　layer　(GDL),　cathode　GDL,　anode　catalyst　layer,　cathode　catalyst　layer,　and　proton　exchange　membrane.　Water　activity,　ionomer　conductivity,　and　output　voltage　are　predicted　by　changing　the　humidity　on　the　anode　side　of　the　fuel　cell.