currently, microwaves are widely used in chemical industry to accelerate chemical reactions. Some research results have shown that microwave heating can significantly accelerate the reaction. Ho wever, there is a need to develop efficient methods to improve the design of microwave applicator in chemistry. In this paper, a numerical model was presented to study the microwave heating on saponification reaction in test tube, where the reactant was considered as a mixture of dilute solution. The coupled electromagnetic field equations, reaction equation (RE) and heat transport equation (HTE) were solved by using finite difference time domain (FDTD) method. To overcome the difficulty of long time calculation with FDTD, two types of techniques were employed. To erify the methods, the temperature rising in the test tube and transmitted power through the transversal electromagnetic (TEM) cell were measured and compared with the computational results. Good agreement can be seen between the measured and calculated results.