For multi-stage continuous crystallization using MSMPR (Mixed Suspension Mixed Product Removal) crystallizers in series, a new method is proposed of calculating the nucleation and crystal growth rates. The method is developed so as to apply to industrial crystallization processes in which each crystallizer has a different retention time and a suspension volume, and in which the whole slurry withdrawn from the previous crystallizer is supplied to the next one. The method is based on analytical solutions of the population balance equation. Using the method, one can calculate the nucleation and crystal growth rates independently and simultaneously from the retention time, the amount of crystals and the crystal size distribution for each crystallizer. The practicability of the method was examined by applying it to three-stage continuous crystallization in a Nissan manufacturing process of melamine. Moreover, the supersaturation and crystal growth rate of melamine were measured by laboratory-scale experiments in order to calculate the operating supersaturation, with which the operation states of each crystallizer in the plant were discussed.