Lipase catalyzed-synthesis of ascorbyl oleate was performed in ionic liquids with addition of salt hydrate pairs for water activity control. The highest yield in the synthesis of ascorbyl oleate (72%) was obtained in [BMIM][BF4] in the presence of the salt pair NaI 2/0, which corresponds to a water activity of 0.3. Purity and chemical identity of 6-O-ascorbyl oleate was confirmed by H-1 and C-13 NMR analysis. (C) 2008 Elsevier Ltd. All rights reserved.