The hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl thioester in water-saturated isooctane was employed as a model system to study the pretreatment effect of Carica papaya lipase on the enzyme performance. In comparison with the result of using deionized water in the pretreatment, improvements in lipase activity and enantioselectivity were achieved when polar organic solvents, pH 8 phosphate buffer, or aqueous solution containing methyl-beta-cyclodextrin, but not NaCl or 18-crown-6, was employed. The lipase pretreated with isopropyl ether was selected as the best lipase and further employed to resolve 2,2,2-trifluroethyl thioesters of (R,S)-fenoprofen, (R,S)-flurbiprofen and (R,S)-ibuprofen.