We investigated a novel, simple method for activating lipases in non-aqueous reaction media. Lipase powders were suspended in n-fatty alcohols and were then hydrated by adding a small amount of water. A paste-like aggregate was recovered from the mixture followed by lyophilization for obtaining activated lipases as dry powders. Lipase activity was evaluated for esterification between myristic acid and methanol in n-hexane. The activated lipases exhibited high esterification activity depending on the experiment conditions during hydration aggregation pretreatment such as the amount of added water, the temperature, the pH of added buffer solutions, and the carbon chain length of the n-fatty alcohols used as pretreatment solvents. Various commercial lipases from different origins could be activated by this method. Changes in lipase conformation induced by the hydration-aggregation pretreatment were studied based on fluorescence and Fourier-transform infrared spectroscopy.