A continuous mixed-suspension mixed-product removal lpar;CMSMPR) crystallizer was used to study the crystallization kinetics and product purity of glutamic acid crystal in pure solution and impure solution with L-phenylanaline as the impurity. Under the assumption that the crystal growth rate was a function of crystal size, the population balance equation was solved to give the crystal growth and nucleation rates by use of the steady-state population density data. The crystal growth and nucleation rates were suppressed by the presence of impurity. The impurity contents in the crystal products, which were analyzed by a HPLC pre-column method, were found to be related to crystal size, supersaturation, and impurity concentration of solution