In this study, a new matrix for immobilization of acetylcholinesterase was investigated by using alginate and kappa-carrageenan. The effects of pH, temperature, storage and thermal stability on the free and immobilized acetylcholinesterase activity were examined. Maximum reaction rate (V-max) and Michael is-Menten constant (K-m) was also investigated for free and immobilized enzymes. For free and immobilized enzymes into Ca-alginate and alginate/kappa-carrageenan polymer blends, optimum pH and temperature was found to be 7 and 30 degrees C, respectively. For free enzyme, maximum reaction rate (V-max) and Michaelis-Menten constant (K-m) values were found to be 6.35 mM and 50 mM min(-1), respectively, the same values for immobilized enzymes were determined as 8.68, 12.7mM and 39.7, 52.9 mM min(-1), respectively. Storage and thermal stability of acetylcholinesterase was increased by as a result of immobilization. (c) 2005 Elsevier B.V. All rights reserved.