Structured lipids were synthesized by acidolysis of olive oil and capric acid with an immobilized lipase (Lipozyme TL IM) from Thermomyces lanuginosus. The acidolysis reaction was carried out by incubating a 1:3 molar ratio of olive oil and capric acid under solvent-free reaction systems at 50 degrees C. The effect of water activity on the incorporation of capric acid was investigated, and the tested water activity range was between 0.22 and 0.80. Capric acid incorporation into triacylglycerols of the olive oil increased as the water activity increased, but the degree of acyl migration also increased. Also, the degree of acyl migration of modified olive oils with a similar degree of incorporation was investigated. High degrees of acyl migration occurred at water activities of 0.22 and 0.32 for the degree of incorporation of ca. 50 mol %. Only 8 h of reaction time was required to achieve incorporation of ca. 50 mol % at a water activity of 0.80, and the lowest acyl migration occurred at the same water activity. These results suggest that acyl migration can be efficiently minimized by a shorter reaction time at higher water activity.