Poly(gamma-glutamic acid) (gamma-PGA) is a material of polymer. Immobilization of Candida rugosa lipase (Lipase AY-30) by covalent binding on,gamma-PGA led to a markedly improved performance of the enzyme. Response surface methodology (RSM) and 3-level-3-factor fractional factorial design were employed to evaluate the effects of immobilization parameters, such as immobilization time (2-6 h), immobilization temperature (0-26 degrees C), and enzyme/support ratio (0.1-0.5, w/w). Based on the analysis of ridge max, the optimum immobilization conditions were as follows: immobilization time 2.3 h, immobilization temperature 13.3 degrees C, and enzyme/support ratio 0.41 (w/w); the highest lipase activity obtained was 1196 U/mg-protein. (c) 2007 Elsevier Ltd. All rights reserved.