For the esterification of 2-(4-ethylphenoxy)propionic acid catalyzed by lipase MY (Candida rugosa) in isopropyl ether containing a suitable amount of water, the enantioselectivity for the reaction has become higher as the reaction temperature increasing. In contrast, the reverse trend of the temperature effect has been observed for lipase AY (Candida rugosa). A model for these temperature dependence has been proposed.