We report a facile one-pot synthesis of Ce x Zr 12x O 2 (0 ¡ x ¡ 1) solid solution nanocrystals using hydrothermal reactions. A direct formation of oxide solid solutions in aqueous solution under pressure at low temperatures was clearly revealed by X-ray diffraction, Raman spectroscopy, and chemical composition analysis of individual nanocrystals using energy dispersive X-ray spectroscopy in scanning transmission electron microscopy mode. Chemisorption behavior of the synthesized nanocrystals was characterized using a hydrogen temperature programmed reduction, which showed a superior lowtemperature activity in Ce x Zr 12x O 2 (0 , x , 1) compared to pure CeO 2 . Furthermore, we investigated the thermal stability of the prepared Ce 0.5 Zr 0.5 O 2 at high temperatures (900 uC-1400 uC) under oxidation and reduction atmosphere. The effect of varying conditions of heat-treatment has given information on the phase transformation in Ce 0.5 Zr 0.5 O 2 from pseudocubic to tetragonal structure under oxidation atmosphere, and to pyrochlore structure under reduction atmosphere.High surface area Ce x Zr 12x O 2 (0 ¡ x ¡ 1) samples were synthesized using a hydrothermal method. Typically, 0.1 M Ce(NO 3 ) 3 ?6H 2 O (Alfa Aesa, 99.99%) and 0.1 M ZrO(NO 3 ) 2 ?xH 2 O