Zwitterionic　layers　immobilized　on　various　surfaces　exhibit　ideal　biocompatibility　and　antifouling　capability,　but　direct　immobilization　of　zwitterionic　molecules　provides　limited　choice　of　surface　charges.　In　this　paper,　the　formation　of　charge　tunable　zwitterionic　polyampholyte　layers　onto　the　surface　of　microfluidic　channels　of　cyclic　olefin　copolymer　by　photochemical　graft　polymerization　of　mixed　acrylic　monomers,　[2-(acryloyloxy)　ethyl]　trimethyl　amrnonium　chloride　and　2-acrylamido-2-methyl-1-propanesulfonic,　under　UV　illumination　was　reported.　With　this　method,　surface　charge　of　the　resulting　modification　layers　could　be　tailored　through　the　initial　monomer　ratio　and　reaction　conditions.　The　incorporation　of　both　monomers　into　the　grafted　layers　was　confirmed　by　X-ray　photoelectron　spectroscopy　(XPS)　and　attenuated　total　reflection　Fourier　transform　infrared　(ATR-FTIR).　The　results　indicate　that　the　modified　layers　are　hydrophilic　with　contact　angles　of　33.0-44.3　degrees,　and　the　isoelectric　points　of　the　modified　layers　can　be　tuned　from　＜3　to　＞9　simply　by　adjusting　the　monomer　ratios.　Elimination　of　the　nonspecific　adsorption　of　proteins　on　the　zwitterionic　layers　thus　formed　was　proved　by　fluorescent　microscopy　and　streaming　potential　measurement.　The　uniformity　of　the　modified　layers　was　verified　through　a　comparison　of　electrophoresis　inside　the　modified　and　native　microchannels.　A　whole　blood　coagulation　time　measurement　was　performed　to　show　its　applicability.