Acrylic　acid　(AA)　and　sodium　styrene　sulfonate　(SSS)　were　grafted　onto　poly(tetrafluoroethylene-co-hexafluoropropylene)　(FEP)　membranes　by　pre-irradiation　method,　and　a　humidity　sensing　membrane　with　strong　acid　and　weak　acid　groups　was　prepared.　Grafting　was　carried　out　by　using　gamma-ray　from　Co-60　at　room　temperature.　Thermal　and　chemical　properties　of　the　grafting　membranes　were　investigated.　Infrared　spectroscopy　analysis　of　the　grafting　membrane　confirmed　the　existence　of　sulfonate　and　carboxylic　acid　groups　in　the　grafting　membranes.　The　thermal　behavior　of　grafting　membranes　was　evaluated　by　TGA,and　the　results　show　that　the　higher　the　grafting　yield　is,the　higher　the　char　residue,　which　indicates　that　the　branch　chains　including　-SO3Na　and　-COOH　provide　catalytic　impetus　to　the　charring.　The　degree　of　crystallinity　of　grafting　membranes　containing　-SO3Na　and　-COOH　groups　decreased　with　the　increase　of　the　grafting　yield.　The　static　contact　angle　with　water　of　the　grafting　membrane　decreases　meanwhile　the　hydrophilicity　of　the　grafting　membrane　increases　with　increasing　the　grafting　yield.　The　electrical　response　properties　of　the　grafting　membrane　to　humidity　was　examined,　too.　The　resistive　of　the　grafting　membrane　changes　linearly　by　3　orders　of　magnitude　over　almost　the　whole　humidity　range　(5%　similar　to　98%　RH).　Furthermore,the　grafting　membrane　exhibits　a　quick　response　(absorption:　less　than　1　min;　desorption:less　than　2　min)　and　small　hysteresis　(less　than　3%　RH).　The　FEP-AA-SSS　membrane　can　be　a　promising　approach　to　the　development　of　new　humidity　sensitive　materials　with　good　sensing　characteristics.