For seeded cooling crystallization, itn is required that the solution is maintained at a supersaturation state within the metastable limit for suppression of homogeneous nucleation. However, the metastable limit is not fixed but time-varying depending upon the solution history. in this study, dynamics of the metastable limit has been exploited. Using the experimental results obtained under various cooling rates, the metastable limit was expressed to have a nonlinear first-order dynamics to a change in the cooling rate. By incorporating this model, an optimal cooling curve was determined for (NH 4)2SO4 crystallization from the (NH 4)2SO4-NH4NO3-H 2O ternary system and experimental verification has been performed.