Lipase-catalyzed transesterification was demonstrated using methyl esters as acyl donors under reduced pressure in an ionic liquid ([bmim]PF6) solvent system. The transesterification of 5-phenyl-1-penten-3-ol took place smoothly under reduced pressure at 27 hPa at 40 degreesC when methyl phenylthioacetate was used as acyl donor in [bmim]PF6, and we succeeded in obtaining the corresponding acylated compound in optically pure form; this makes it possible to use lipase repeatedly because there was no drop in the reaction rate despite three repetitions of the process.