A novel framework has been proposed for optimizing batch cooling crystallization operation. The optimization strategy is effective for highly non-linear and dynamic mathematical systems such as batch cooling crystallization systems. The proposed framework can implement constrained multivariable optimization without the tendency of being trapped into local optima. Variables that can be optimized simultaneously include the cooling profile, seed size, mass of seeds, batch time, initial and final temperatures. Optimizations have been implemented on both seeded and unseeded processes of the citric acid-water system. The optimized operation leads to improvements that otherwise cannot be attained by using conventional approaches. Optimization results also suggest that seeding can increase the flexibility of the operation. (C) 2003 Elsevier Ltd. All rights reserved.