The heat generation behavior of liquid-liquid heterogeneous reactions when stirring is instantly re -started after phase separation is investigated using a reaction calorimeter. An empirical equation of the heat release rate is introduced on the assumption that the transfer rate of reactant to the continuous phase and the reaction rate are balanced after re-start stirring. As experimental values of the maximum heat release rate under Various experimental conditions of sulfonation of toluene and neutralization of acetic acid and sodium hydroxide are applied to the proposed equation, a good correlation is found between the maximum heat release rate and the size of the interfacial area for each reaction. Since the mass transfer coefficient of the neutralization obtained by this equation agrees well with the literature value, it is found that the mass transfer rate can be determined by measurement of the heat release rate with a reaction calorimeter. Furthermore, the heat release rate vs. time curves after re-start stirring under the various conditions are calculated using the proposed equations of each reaction, and the calculated results show good agreement with the experimental values when the dispersed phase is completely dispersed into the aqueous phase.