As　an　important　performance　diagnosis　tool,　in-situ　measurement　of　current　distribution　in　PEM　fuel　cells　is　helpful　for　better　understanding　of　internal　transport　phenomena　and　optimization　of　fuel　cell　structures　and　operating　parameters.　With　a　specially　developed　current　distribution　measurement　gasket,　the　effects　of　reactant　gas　flow　rates　on　the　current　distribution　in　a　PEM　fuel　cell　with　single　serpentine　flowfield　were　investigated.　Experimental　results　show　that　insufficient　hydrogen　or　air　leads　to　decreased　current　density　along　the　gas　flow　direction.　Higher　reactant　gas　flow　rate　favors　not　only　the　local　performance　but　also　the　homogeneity　of　current　distribution.　But　current　distribution　almost　ceases　to　change　with　further　increase　of　hydrogen　flow　rate　when　it　reaches　certain　value.