Abstract La 2M 2O 7 (M = Ti, Zr) powders have been hydrothermally synthesized from the double hydrous oxides La 2O 32MO 2nH 2O using KOH as the mineralizer. The effects of factors such as the KOH concentration, reaction temperature, and time were investigated. Moreover, the related phases perovskite La 2/3TiO 3−λ (λ = 0.000–0.024) and fluorite La 2Zr 2O 7 as well as pyrochlore La 2Zr 2O 7 powders were prepared for the first time by the hydrothermal method. Further insight was gained through X-ray diffraction, transmission electron microscopy, infrared, and other techniques. The moderate conditions give excellent ceramics powders, and the resulting particles, with a simple mode of size distribution, appear at low agglomeration.