In this study, alpha-chymotrypsin was immobilized via physical entrapment within large, uniformly spherical, and thermally reversible poly (N-isopropylacrylamide) [poly(NIPAM)] beads. The gel beads were prepared in an aqueous dispersion medium by using Ca-alginate gel as the polymerization mold. In this preparation, potassium persulfate/tetramethylethylenediamine and sodium-alginate/calcium chloride were used as the redox initiator and the stabilizer systems, respectively. Thermoresponsive poly(NIPAM) gel beads 3 mm in size and including alpha-chymotrypsin were produced by the proposed procedure. The use of an aqueous bead-forming medium did not cause significant enzyme leakage during the preparation of enzyme-gel beads. Michaelis-Menten kinetics was used to define the behaviors of enzyme-gel beads prepared with different enzyme loadings. The Lineweaver-Burk plot indicated that the enzyme-gel system had a reasonably higher K-m value relative to that of free enzyme due to the internal mass transfer resistance against the substrate diffusion. The enzyme-gel system exhibited the maximum activity at 30 degrees C due to the thermoresponsive character of the carrier matrix. However, the maximum activity with the free enzyme was observed at 40 degrees C.