N-Isopropylacrylamide/acrylamide copolymer hydrogels were prepared with crosslinking agent by free radical polymerization. Swelllng/shrinking ratio, amount of water uptake, transmittance, and the change of phase transition temperature of copolymer hydrogel were studied. Invertase, sucrose hydrolase, was immobilized within N-Isopropylacrylamide/acrylamide copolymer hydrogels with different content of acrylamide and its enzymatic activities as a function of temperature were also studied. As the acrylamide content increased, swelling/shrinking ratio, amount of water uptake, and the phase transition temperature were increased. Swelling/shrinklng ratios of copolymer hydrogel were increased up to 7, 20, 80% when the temperatures were 20, 30 and 40℃, respectively. Amounts of water uptake by copolymer hydrogel at 30℃, were increased as much as 11, 19, 22 and 44% when the contents of acrylamide was 3, 5, 7 and 10%, respectively. Phase transition temperature of N-isopropylacrylamide hydrogel is 32∼34℃. As the content of acrylamide increased, phase transition temperature of copolymer hydrogel was increased up to 53℃. Enzymatic activities of invertase immobilized within copolymer hydrogels with different content of acrylamide were switched on and off by the change of reaction temperature below and above their respective phase transition temperature of copolymer hydrogel.