An experimental design was employed to optimize the refolding conditions of a recombinant lipase from Pseudomonas sp. which expressed as inclusion bodies in Escherichia coli. The effects of several variables on the refolding and activation of the enzyme has been studied. Because of the complexity of the reaction with respect to the number of parameters that can affect the refolding efficiency, 2(6-1) half-fractional factorial design (H-FFD) was employed for initial screening of the factors, potentially influencing the response. Experiments were performed in triplicate at two levels. Subsequently, the selected factors were subjected to response surface methodology (RSM) with a four factor-five coded level central composite design (CCD), using Quadratic model for obtaining the optimum values for the factors. The adequacy of the calculated model was confirmed by the coefficient of determination (R-2) and F value of 0.89 and 9.12, respectively. The optimized condition for the refolding was obtained in the refolding buffer containing unfolded lipase (10 mu g/ml) and foldase (3 mu g/ml) in combination with glycerol (10%), NaCl (1 M) and sucrose (0.5 M). Using chemicals in combination with foldase under the optimal condition exhibited a 50% increase in refolding yield over the conventional method. (C) 2009 Elsevier Inc. All rights reserved.