A mathematical model that considers the interactive effects of the segregation and mixing of the crystals is developed in this paper to describe the behavior of crystal growth in a fluidized bed crystallizer operated in a batch mode. It is assumed that the liquid phase moves upward through the bed in plug flow, and the solid phase is represented by a series of equal-sized ideal mixed beds of crystals. The crystals in each bed are completely mixed; however, the crystals in different beds are totally segregated. This concept corresponds to a one-parameter method, and the one parameter of this model is the number of mixed beds of crystals in series (M). The developed model can determine the crystal size, the solution concentration, and the bed voidage in each mixed bed of crystals during the operation. Subsequently, it can predict the weight-average size ((L) over bar) and the coefficient of variation (CV) of the resulting crystals in a fluidized bed crystallizer.