The effect of soaking treatment before cooking on the hardness of soybeans and red kidney beans stored at 37 °C/75 % RH (aged beans) was evaluated by kinetic analysis using the softening rate constant. Based on the analysis results, softening behavior was separately examined as “softening due to water absorption” and “softening due to heating”, making it possible to predict the heating time and to quantitatively evaluate the effect of soaking treatment on hardness during cooking of beans. Interestingly, in both aged beans, prolonged soaking time remarkably suppressed softening during subsequent heating. In addition, in both aged beans, when the soaking time was longer, the value of the softening rate constant k_s1 for pre-soaked beans decreased and the difference in the predicted heating time between pre-soaked and un-soaked beans was reduced. These results indicated that soaking treatment before cooking is not recommended for stored beans, as it suppresses their softening during cooking.