An isothermal hydrothermal reaction scheme has been developed to produce pure, ultrafine crystalline lanthanum titanate from lanthanum nitrate-titanium tetrabutyloxide-wateralcohol. It was found that the pH of the hydrothermal reaction medium and the initial [La]/[Ti] (molar ratio) were critical factors in forming stoichiometric La2/3TiO3 . By varying the pH of the reaction medium, different end products could be obtained. With [La]/[Ti]=0.5, the as-prepared La2/3TiO3 was in the cubic perovskite phase, and the structure did not change when the temperature was increased from room temperature to as high as 1000 °C. The optimum synthesis conditions including the ratio of [La]/[Ti], the concentration of NaOH and the lowest synthesis temperature were investigated. Under hydrothermal conditions, the La2 O3 -3TiO2 system can tolerate the solid solubility of TiO2