Surface　charge　and　hydrophilicity　of　microchannels　are　very　important　for　lab-on-a-chips　devices.　A　facile　way　for　in-channel　tuning　of　both　hydrophilicity　and　surface　charge　of　microchannels　of　cyclic　olefin　copolymer　chips　with　photochemical　grafting　was　verified.　Six　acrylic　monomers　with　anionic,　neutral　and　cationic　functional　groups,　respectively,　were　selected　to　implement　different　surface　charges.　Influence　of　experimental　conditions,　such　as　UV　intensity,　irradiation　time,　monomer　concentration　and　reaction　temperature,　were　investigated　based　on　the　contact　angles　of　pure　water　on　the　modified　surfaces.　Surface　charges　of　the　modified　channels　were　confirmed　with　streaming　potential　measurement.　The　modified　microchannels　were　used　in　the　electrophoretic　separation　of　four　fluorescein　isothiocyanate　labeled　amino　acids.　The　results　indicated　that　photochemical　grafting　could　be　used　to　introduce　hydrophilic　layer　of　predefined　surface　charge　onto　the　channel　surface　within　60　s　and　good　electrophoretic　separation　could　be　obtained　inside　the　modified　channels,　which　implied　that　the　method　could　be　used　for　tailoring　the　surface　of　microchannels　of　lab-on-a-chip　devices.　(c)　2012　Elsevier　B.V.　All　rights　reserved.