The　water　flooding　and　two-phase　flow　of　reactants　and　products　in　cathode　flow　channels　(0.8　mm　in　width,　1.0　mm　in　depth)　were　studied　by　means　of　transparent　proton　exchange　membrane　fuel　cells.　Three　transparent　proton　exchange　membrane　fuel　cells　with　different　flow　fields　including　parallel　flow　field,　interdigitated　flow　field　and　cascade　flow　field　were　used.　The　effects　of　flow　field,　cell　temperature,　cathode　gas　flow　rate　and　operation　time　on　water　build-up　and　cell　performance　were　studied,　respectively.　Experimental　results　indicate　that　the　liquid　water　columns　accumulating　in　the　cathode　flow　channels　can　reduce　the　effective　electrochemical　reaction　area;　it　makes　mass　transfer　limitation　resulting　in　the　cell　performance　loss.　The　water　in　flow　channels　at　high　temperature　is　much　less　than　that　at　low　temperature.　When　the　water　flooding　appears,　increasing　cathode　flow　rate　can　remove　excess　water　and　lead　to　good　cell　performance.　The　water　and　gas　transfer　can　be　enhanced　and　the　water　removal　is　easier　in　the　interdigitated　channels　and　cascade　channels　than　in　the　parallel　channels.　The　cell　performances　of　the　fuel　cells　that　installed　interdigitated　flow　field　or　cascade　flow　field　are　better　than　that　installed　with　parallel　flow　field.　The　images　of　liquid　water　in　the　cathode　channels　at　different　operating　time　were　recorded.　The　evolution　of　liquid　water　removing　out　of　channels　was　also　recorded　by　high-speed　video.　(c)　2005　Elsevier　B.V.　All　rights　reserved.