Well-crystalline CeO2-x nanotubes are synthesized via a mild hydrothermal reaction route using cerium nitrate and ammonium hydroxide as reactants. The CeO2-x nanotubes have the same structure as the bulk CeO2 but larger lattice parameter. The measurement of the ratio of M5/M4 edge shows the valence reduction of cerium ions for the CeO2-x nanotubes.