Solubilities of 6APA in water at different pH and temperatures are measured. A three parameter model is proposed for predicting the aqueous solubility of this amino acid. Predicted values are in good agreement with the experimental data. The model may be used for quick and accurate evaluation of the aqueous solubility of other simple ampholytes. The proposed correlation is combined with the population balance and kinetic equations for predicting the optimum pH profiles required to maintain a constant supersaturation in a batch crystallizer. The suggested policy leads to a more uniform crystal size distribution for 6APA with C.V of 23%.