La2M2O7 (M = Ti, Zr) powders have been hydrothermally synthesized from the double hydrous oxides La(2)O(3)2MO(2)nH(2)O 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 La2/3TiO3-lambda (lambda = 0.000-0.024) and fluorite La2Zr2O7 as well as pyrochlore La2Zr2O7 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.