A lipase-catalyzed condensation reaction in an organic solvent is a promising means of synthesizing esters. Reaction equilibrium constant, which is usually defined on the basis of reactant concentration, is an important parameter for estimating equilibrium yield. It is shown that the constant is markedly, affected by some factors, such as the hydration of a sugar substrate and the interaction of a reactant with a solvent. To reasonably design the reaction system or determine the reaction conditions, attention should be paid to these factors. From the viewpoint of kinetics, substrate selectivity for carboxylic acids also numerically correlates to the electrical and steric properties of these acids. Reactor systems for continuously producing esters through an immobilized-lipase-catalyzed condensation reaction are developed.