Microbial lipase from Candida rugosa immobilized into porous chitosan beads was tested for esterification selectivity with butanol and different organic acids (C2-C12), and butyric acid and different aliphatic alcohols (C2-C10). After 24 h, the acids tested achieved conversions of about 40-45%. Acetic acid was the only exception, and in this case butanol was not consumed. Different alcohols led to butyric acid conversions >40%, except for ethanol, in which case butyric acid was converted only 26%. The system's butanol and butyric acid were selected for a detailed study by employing an experimental design. The influence of temperature, initial catalyst concentration, and acid:alcohol molar ratio on the formation of butyl butyrate was simultaneously investigated, employing a 23 full factorial design. The range studied was 37-50degreesC for temperature (X-1), 1.25-2.5% (w/v) for the catalyst concentration (X-2), and 1 and 2 for the acid:alcohol molar ratio (X-3). Catalyst concentration (X-2) was found to be the most significant factor and its influence was positive. Maximum ester yield (83%) could be obtained when working at the lowest level for temperature (37degreesC), highest level for lipase concentration (2.5% [w/v]), and center level of acid:alcohol molar ratio (1.5). The immobilized lipase was also used repeatedly in batch esterification reactions of butanol with butyric acid, revealing a half-life of 86 h.