A　two-phase　flow　model　for　a　proton　exchange　membrane　(PEM)　fuel　cell　is　developed.　The　model　is　based　on　the　mixture　flow　model　and　the　unified　approach　is　used.　Instead　of　using　a　separate　model　for　the　catalyst　layer,　the　catalyst　layers　are　now　included　in　the　respective　unified　domains　for　the　cathode　and　anode,　thus　continuity　boundary　conditions　at　the　interface　between　the　catalyst　layer　(CL)　and　the　gas　diffuser　layer　(GDL)　are　no　longer　needed.　The　model　couples　the　flows,　species,　electrical　potential,　and　current　density　distributions　in　the　cathode　and　anode　fluid　channels,　gas　diffusers,　catalyst　layers　and　membrane　respectively.　Furthermore,　the　two-phase　flow　model　is　also　used　in　the　anode　side,　and　the　momentum　transfer　between　the　liquid　and　gas　phases　due　to　phase　change　is　taken　into　consideration.　Experiments　have　been　conducted　to　study　the　performances　of　a　PEM　fuel　cell　and　the　results　are　used　to　improve　and　validate　our　model.　The　modeling　results　of　polarization　curves　compared　well　with　the　experimental　data.　The　model　is　used　to　study　the　influences　of　fuel　cell　operating　temperature,　operating　pressure　and　humidification　temperature　on　the　oxygen,　vapor　and　liquid　water　transports,　as　well　as　fuel　cell　performances.　(c)　2004　Elsevier　B.V.　All　rights　reserved.