Water　management　is　important　for　improving　the　performance　and　stability　of　proton　exchange　membrane　fuel　cells　(PEMFCs)　for　space　applications.　An　in　situ　visual　observation　was　conducted　on　the　gas　liquid　two-phase　flow　in　the　cathode　channels　of　a　PEMFC　in　short-term　microgravity　condition.　The　microgravity　environment　was　supplied　by　a　drop　tower.　A　single　serpentine　flow　channel　with　a　depth　of　2　mm　and　a　width　of　2　mm　was　applied　as　the　cathode　flow　field.　A　membrane　electrode　assembly　comprising　of　a　Nafion　112　membrane　sandwiched　between　gas　diffusion　layers　was　used.　The　anode　and　cathode　were　loaded　with　1　mg　cm(-2)　platinum.　The　PEMFC　shows　a　distinct　operating　behavior　in　microgravity　because　of　the　effect　of　gravity　on　the　two-phase　flow.　At　a　high　water　production　regime,　cell　performance　is　enhanced　by　4.6%　and　the　accumulated　liquid　water　in　the　flow　channel　tends　can　be　removed　in　microgravity　conditions　to　alleviate　flooding.　At　a　low　water　production　regime,　cell　performance　deteriorates　by　6.6%　and　liquid　aggregation　occurs　in　the　flow　channel　because　of　the　coalescence　of　dispersed　water　droplets　in　microgravity　conditions,　thus　squeezing　the　flow　channel.　The　operating　behavior　of　PEMFC　in　microgravity　conditions　is　different　from　that　in　normal　gravity　conditions.　Further　studies　are　needed　on　PEMFC　operating　characteristics　and　liquid　management　for　space　applications.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.