By using the redox reaction between Ce(IV) and terminal -CH2OH groups of polyethylene oxide(PEO), block copolymers composed of poly(N-isopropylacrylamide)(PNiPAAm) and poly(ethylene oxide) was prepared. The aqueous solution of the block copolymers exhibited thermal phase transition and the phase transition temperature of these block copolymers became higher than the PNiPAAm homopolymer.