For pharmaceutical crystallization design and control, the kinetics of nucleation and growth of crystals are significant parameters, especially for the system exhibiting polymorphic transformation. In this study, imatinib mesylate, whose solubility, nucleation and growth kinetics are lacking in the literature, was thoroughly explored in the aspects of characterization, solubility and polymorphic transformation, and evaluation of nucleation and growth rate. Two forms of imatinib mesylate, alpha and beta, were characterized by X-ray powder diffraction, scanning electron microscopy and differential scanning calorimetry. The solubility measurement of the two forms was performed with ultraviolet-visible spectroscopy in three solvents from 278.15 to 333.15 K at atmospheric pressure. The results indicated the beta-form is more stable in methanol, 1-propanol, and 2-propanol under the experimental condition. The solubility order is methanol > 1-propanol > 2-propanol. The solvent-mediated polymorphic transformation (SMPT) of imatinib mesylate from alpha-form to beta-form was studied with the in-situ Raman spectroscopy and conductivity meter. It is found that the SMPT process of imatinib mesylate from alpha-form to beta-form in methanol is controlled by nucleation and growth of beta-form. Finally, the nucleation and grow rate of beta-form of imatinib mesylate were estimated by minimizing the difference between the calculated and experimental solution concentration with MATLAB optimization function.