The growth rate of the stable polymorph A and the dissolution rate of the unstable polymorph B of L-histidine (L-his) in aqueous solution were experimentally determined at varying temperatures. The growth and dissolution kinetics were measured by means of desupersaturation and deundersaturation techniques, respectively. Both the growth and dissolution rates increase with higher temperature. At all temperatures studied, the dissolution rate of form B is faster than the growth rate of form A, indicating that the solution-mediated transformation of the polymorphs of L-his is likely to be controlled by the growth rate of form A. Both kinetics of the polymorphs of L-his will be used to characterize the polymorphic transformations and the overall crystallization rate of L-his.