H+/Na+ion-exchange in Ti(HP04)2.2H20 (γ TiP) was studied. The exchange isotherm, titration and hydrolysis curves at 25°C were obtained. In initially acidic or neutral solutions the 25% of the material exchange capacity was reached. The half-exchanged phase was obtained by additions of stoichiometric amounts of NaOH, with hydrolysis lower than 3% and at acidic equilibrium pH. For additions of NaOH over 4.0 me/g Y-TiP conversions higher than 50% were reached with an increase in the values of the equilibrium pH and the hydrolysis. The evolution of the solid was followed by X-ray diffraction. The substituted phases of samples dried in air at room temperature showed the following hydration degrees: ----H N ----------------------- conversion phase stored over P205 was dehydrated originating H1-5Na0.5 When i t is heated at 80°C-200°C i t transformed i n t o mixtures o f iTFi ( 9. 1 A ) and HNa (10.1 Å ).