The dissolution profiles of the complexes of sulfamethoxazole (SMO) and sulfamonomethoxine (SMM) with 18-crown-6 (1, 4, 7, 10, 13, 16-hexaoxacyclooctadecane, 18-C-6) involving simultaneous decomplexation were investigated kinetically in detail by a dispersed amount method and a stationary disk method in comparison with those of intact SMO and SMM. The dissolution rates of the complex before and after the phase change, R_c and R_o, respectively, the saturated concentrations of complex and intact drug, C_sc and C_so, respectively, the rate constant of crystallization process, k_r, and the dissolution rate constant, k_t, were calculated by the stationary disk method. Analyzing the values of k_r and k_t obtained at various temperatures, the activation energies of crystallization and dissolution process were determined. The activation energy of crystallization process seemed small compared with the past data reported on organic medicinals.