Magnetically separable polyaniline nanofibers were synthesized using a mixture of aniline solution and iron oxide; the nanofibers comprised of crosslinked linear polymers that could be separated from the reaction solution by using magnets. The covalently attached and aggregated lipases retained a high degree of stability, were easily recovered from the enzyme solution, and could be used repeatedly. The enzyme activity of the dispersed magnetic nanofibers was more than 80%, of the original activity even under room temperature and shaking conditions for 32 days. The highly active and stable immobilized lipase (LP) was then used in an enantioselective esterification reaction, and 18% of the prophilic ester of ibuprofen, a chirally selective compound, was synthesized from racemic ibuprofen following a reaction for 96 h. (c) 2008 Elsevier Inc. All rights reserved.