Fuel　Cells　have　attracted　much　attention.　Liquid　fed　direct　methanol　fuel　cells　(DMFCs),　which　have　many　important　advantages　over　such　as　the　easy　storage　and　refilling　of　the　aqueous　methanol　solution,　are　considered　to　be　good　choices　for　small　mobile　devices.　Water　and　carbon　dioxide　are　the　sole　fuel　oxidized　byproducts.　The　anode　side　of　liquid　fed　DMFC　is　a　two-phase　system　primarily　consisting　of　methanol　solution　and　carbon　dioxide　bubbles.　In　this　paper,　a　transparent　direct　methanol　fuel　cell　was　designed　and　fabricated　for　investigations　of　two-phase　flow　characteristics　in　anode　serpentine　flow　field.　In　situ　observations　of　the　carbon　dioxide　bubbles　and　two-phase　flow　patterns　inside　the　flow　field　were　made.　The　effects　of　cell　current,　methanol　solution　flow　rate　and　methanol　solution　mole　concentration　on　the　flow　patterns　and　cell　performance　were　studied,　respectively.　Experimental　results　indicate　that　the　electrochemical　reaction　and　two-phase　flow　characteristics　interacted　each　other.　The　mean　size　of　CO2　bubbles　and　the　gas　void　fraction　increased　with　increase　in　current　density.　The　typical　flow　patterns　are　bubbly　flow　and　slug　flow.　At　the　upside　down　U　type　location　of　the　serpentine　channel,　long　slug　bubbles　easily　formed　and　blocked　the　channel.　The　gas　void　fraction　decreased　with　increase　in　methanol　solution　flow　rate.　The　methanol　solution　mole　concentration　influences　the　two-phase　flow　slightly.　©　2010　by　ASME.