The transesterification of triglyceride with methanol using an alkali catalyst was experimentally measured, and the obtained equilibrium constants were analyzed by the van't Hoff model. The constant for the conversion of triglyceride to diglyceride was the smallest. The standard enthalpies of formation in the transesterification were measured to be positive, i.e., the reaction is endothermic. Next, the transesterification using the countercurrent multistage reactor system was computationally simulated with the equilibrium stage model, in which the equilibrium constants obtained above were used. The concentrations of the triglyceride remaining in the biodiesel fuel product drastically decreased by the reactor staging, and consequently the reaction temperature and the required amount of methanol could be reduced. The transesterification by the countercurrent multistage reactor was found to be attractive because of the efficient production of the biodiesel fuel.