Diblock copolymer P(4-ASt-b-NIPAm) with well-defined structure and narrow molecular-weight distri-bution (Mw/Mn=1.28) was synthesized by reversible addition-fragmentation transfer (RAFT) polymeriza-tion using poly(4-acetoxystyrene) P(4-ASt) and N-isopropylacrylamide (NIPAm) as monomers. The ace-tyl groups in the chain of P(4-ASt-b-NIPAm)) were selectively hydrolyzed by hydrazine hydrate to obtain diblock copolymer P(4-VPh-b-NIPAm). Copolymer P(4-VPh-b-NIPAm) was characterized by 1HNMR, FTIR and GPC. The aggregation behavior and temperature response of P(4-VPh-b-NIPAm) aqueous solu-tion were studied by fluorescence spectrum, transmittance method and DLS. The results showed that co-polymer P(VPh-b-NIPAm) could self-assemble into micelles using P(4-VPh) as core and PNIPAm as shell in aqueous solution and the critical micelle concentration (CMC) was 0.015 g/L. The average parti-cle size was about 137 nm at room temperature and the lower critical solution temperature (LCST) was 31.2℃. Horseradish peroxidase (HRP) catalyzed cross-linking of P(4-VPh) core to prepare core-crosslinked micelles with an average particle size of 119 nm. TEM showed that dry core-crosslinked micelles were spherical with particle size of 60~100 nm. The aqueous solution of core-crosslinked mi-celles had good stability and temperature response. Its phase transition temperature ranged from 32℃ to 36℃ and its LCST was about 34.9℃. The average diameter of core-crosslinked micelles decreased from 119 nm to 93 nm with increasing temperature from 25℃ to 37℃.