BACKGROUND: Penicillin G acylase (PGA) has been used extensively in the beta-lactam antibiotics industry. As a biocatalyst, it is better to use immobilized enzymes than free enzymes, therefore, the immobilization of PGA on a composite carrier consisting of an adsorbent resin and biocompatible chitosan were investigated. RESULTS: First, FT-IR, BET and SEM analysis confirmed the structure of the composite carrier. Then, the immobilization process was optimized. The activity of the immobilized PGA on the chitosan-resin (IP-CsR) was about 1300 U (g dry carrier)(-1) with a protein loading of about 27mg (g dry carrier)(-1). Compared with the immobilized PGA on unmodified resin (IP-R), the specific activity of IP-CsR was enhanced about 2-fold. The operational, thermal and pH stability were investigated. IP-CsR maintained more than 75% initial activity after 35 cycles, while IP-R was active for only 10 cycles. The half-life at 50 degrees C increased from 75 to 300 min and the most stable pH was changed from 8.0 to 5.5. CONCLUSION: A novel composite carrier containing a biocompatible chitosan was very effective for PGA immobilization. (C) 2008 Society of Chemical Industry