Colored potassium dihydrogen phosphate (KDP) crystals from a dye (sky blue) solution were produced in a mixed suspension mixed product removal (MSMPR) crystallizer. The crystal size distribution (CSD) of the KDP crystals was correlated by a size-dependent growth rate model. The growth rate increased with crystal size, but it decreased as the residence time increased. Two different concentrations of dye in the solution were examined for MSMPR crystallization of KDP crystals. The colored crystals from the solution with low dye-concentration generated regular-shaped KDP crystals. The dye distribution coefficient into the regular-shaped KDP crystals was less than unity. However, the colored crystals from the solution with high dye-concentration formed the special-shaped KDP crystals having no (10 0) sector. The dye distribution coefficient into the special-shaped KDP crystals from the dye solution was larger than unity. The dye distribution coefficient as a function of crystal size was presented, and then the relationship between the aspect ratio of the morphology of KDP crystals and dye distribution coefficient was discussed. As a result, a distribution model of dye impurity in KDP crystals for an MSMPR crystallizer could be first proposed in this work. (C) 2004 Elsevier B.V. All rights reserved.