A thermodynamic model was established to determine ion-exchange conditions for the synthesis of potassium hexatitanate (K(2)O(.)6TiO(2)) and titanium dioxide (TiO2) from potassium tetratitanate (K(2)O(.)4TiO(2)) fiber. In the proposed model equilibrium species in the solid phase and corresponding ion-exchange equilibrium constants at 298.15 K were determined from the experimental data of Sasaki et al. [Inorg. Chem. 24 (1985) 2265]. In order to verify the proposed model, prediction results were compared with experimental data determined in literature and those measured in this work. The comparison shows a good agreement. Based on this, the proposed model was also used to predict more extensive suitable conditions for the synthesis of K(2)O(.)6TiO(2) and TiO2.