Two-phase　transport　is　essential　for　water　and　thermal　management　of　passive　direct　methanol　fuel　cells　(DMFCs).　This　paper　develops　a　three-dimensional　(3D),　transient,　isothermal　and　two-phase　mixture　model　and　investigates　the　mass　transfer　characteristic　in　the　air-breathing　cathode　of　a　direct　methanol　fuel　cell.　The　velocity　and　volume　fraction　of　species　inside　the　fuel　cell　along　with　the　process　of　electrochemical　reaction　are　studied.　The　effects　of　several　key　parameters　such　as　porosity　of　porous　medium,　current　density　and　cell　operation　pressure　are　investigated　to　discuss　mass　transfer　characteristic　in　the　passive　DMFC　cathode.　The　numerical　simulation　results　indicate　that　cathode　catalyst　layer　porosity　has　definite　effects　on　oxygen　transfer　and　removal　of　water.　It　is　also　found　that　an　adequate　current　density　and　appropriate　cathode　pressure　could　facilitate　a　more　quickly　removal　of　water　from　the　cathode　to　the　ambient.　Copyright　(C)　2013,　Hydrogen　Energy　Publications,　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.