Novel　well-defined　coil-comb　polycationic　brushes　were　synthesized　via　atom　transfer　radical　polymerization　and　used　as　gene　carriers.　The　side　chains　of　the　comb　block　were　composed　of　star　polymers　with　cyclodextrin　as　the　core　and　poly(2-dimethylaminoethyl　methacrylate)　(PDMAEMA)　as　the　arm.　The　DNA　binding　capability　of　the　brushes　was　characterized,　and　the　cytotoxicity　and　transfection　efficiency　were　investigated　in　COS-7　and　293T　cells.　With　such　super-high　grafting　density　of　PDMAEMA,　the　brushes　effectively　condensed　pDNA　into　spherical　nanoparticles　of　100-200　nm　in　size　and　exhibited　significantly　higher　transfection　capability　compared　to　the　single　star　polymer.　In　some　cases,　they　also　showed　comparable　or　higher　transfection　efficiency　and　lower　cytotoxicity　than　PEI25K.　The　results　indicated　that　these　brushes　had　good　promise　for　the　potential　gene　therapy.　Actually,　this　work　also　provides　a　versatile　method　to　prepare　polymer　brushes　with　such　unique　structure　and　flexible　functionality,　which　has　wide　applications　in　the　fields　of　biomedical　devices,　electronics　and　catalysts.