The issues regarding the design and implementation of on-line optimal control strategies of crystal properties in nonisothermal antisolvent crystallization processes to control particles' mean size and standard deviation are dealt. The one-dimensional Fokker-Planck equation is used to represent the dynamic characteristics of the crystal growth and generate iso-mean and iso-standard deviation curves. Using controllability tools it is demonstrated that the system is ill conditioned in the whole operational range, posing limitations on the achievable control performance. To circumvent the problem, a control strategy is formulated by pairing crystals' mean size with antisolvent feed rate and manipulating temperature to control the standard deviation. A novel digital image-texturing analysis approach is discussed and implemented to track crystals' size distribution along the experiment and providing the on-line information for further feedback control action. Subsequently, alternative control strategies are implemented and tested to achieve a desired crystal size distribution. (c) 2015 American Institute of Chemical Engineers AIChE J, 61: 2188-2201, 2015