A copolymer of methacrylic acid (MAA) and N-isopropyl acrylamide (NIPAM) was used as a novel, reversibly soluble-insoluble support whose solubility changes depending on the temperature of the solution. Amylase (Dabiase K-27) immobilized covalently on the thermo-responsive polymer showed good solubility response : the immobilized enzyme (D-MN) was in a soluble state below 32 degrees C, but insoluble above 42 degrees C. D-MN in a soluble state has a high specific activity for the hydrolysis of soluble or uncooked starch. The solubility response of D-NM to changes in the temperature of the solution was more sensitive when 0.5% NaCl was added to a buffer solution (pH 4.5) with D-MN than in the buffer solution without NaCl D-MN was used successively for repeated hydrolysis reactions of soluble and uncooked starches, in which D-MN was insolubilized either by changing the temperature of the reaction mixture from 30 degrees C to 36 degrees C with 0.5% NaCl or by adjusting the NaCl concentration of the reaction mixture from O% to 1% at 30 degrees C. In the repeated hydrolysis, glucose was produced successively from the soluble and uncooked starches, and D-MN could be repeatedly used after being recovered from the reaction product by centrifugation at the end of each batchwise hydrolysis.