A temperature-responsive N-isopropylacrylamide (NIPAAm) oligomer with an ester functional end group and a molecular weight of 3300 was prepared by chain-transfer polymerization using beta-mercaptopropionic acid and subsequently activated by N-hydroxysuccinimide (NHS). This oligomer was coupled to alpha-chymotrypsin to yield a thermo-sensitive reversibly soluble-insoluble oligomer-enzyme conjugate, which is water-soluble at temperatures below 34 degrees C and that precipitates above 36 degrees C. The conjugated enzyme showed higher activity, and improved thermal stability compared with native enzyme. Kinetic properties and optimum conditions for activity were compared with those of native enzyme. More than 93% enzyme activity of the conjugate was recovered after eight cycles of thermal-induced precipitation. The oligomer-enzyme complex was used for repeated hydrolysis of casein; the biocatalyst was recovered between runs by thermal-induced precipitation and showed good stability.