Microbial lipase produced by Rhizopus sp. was tested for the synthesis of citronellyl butyrate and citronellyl valerate. Lipase showed more ability to catalyze the synthesis of citronellyl butyrate. This process was optimized using response surface methodology (RSM) based on a five-level, two variable central composite rotatable design (CCRD). The optimum conditions were molar ratio of 2.41:1 (alcohol: acid) and lipase amount of 6.12% (w/w) and the yield achieved 100% (molar conversion) in 48 It. Lipase was also immobilized onto celite and its activity improved, leading to 100% molar conversion in 24 h. However, immobilized lipase did not exhibited operational stability after a few reaction cycles. (c) 2005 Elsevier Ltd. All rights reserved.