The stability of acid phosphatase immobilized on composite beads was studied. The beads were prepared from equal weights of cuttlebone chitosan and activated clay and were cross-linked with glutaraldehyde. The immobilized enzyme maintained 90% of its original activity after 50 times of reuse. The immobilized acid phosphatase revealed acceptable thermal and pH stabilities over a broad experimental range. Thermal deactivation of immobilized enzyme was also examined by first-order kinetics and the deactivation energy was determined. The kinetics of a model reaction catalyzed by the immobilized acid phosphatase was finally investigated by the Michaelis-Menten equation. (C) 2003 Elsevier Ltd. All rights reserved.