Solvent-mediated transformation of disodium guanosine 5'-monophosphate (5'-GMPNa(2)) from amorphous to hydrated crystal phases was studied. The SMT process is dominated by the dissolution of the amorphous form and nucleation and growth of the crystal polymorph. The kinetic estimation based on population balance equation was carried out according to experimental data, including polymorphic fraction in the solid phase, solute concentration, and crystal size distribution. Furthermore, independent seeded batch experiments were carried out to estimate the kinetic parameters. The experimental data showed that the nucleation and growth of the crystal polymorph occurred shortly after the dissolution of the amorphous form. The 12 0 estimated growth, nucleation, and dissolution rates indicated that the solution-mediated transformation was governed by the nucleation and growth of crystal polymorph. We believe that the results hold great importance toward understanding the transformation process of S'-GMPNa(2), which provides theoretical guidance for producing its specific forms, and possibly those for other pharmaceuticals and chemicals as well.