Based on cause and effect rather than experiment data, zirconium hydroxide (Zr(OH)(4). nH(2)O) is always considered as hydrous zirconia (ZrO2. nH(2)O). With the aid of nitric acid, XPS, XRD, XPF, and TGA, some differences between them have been confirmed. It is found that in contrast to zirconium hydroxide (the binding energy of zirconium = 183.6 eV), hydrous zirconia does not dissolve in nitric acid. The chemical properties of zirconium (181.8 eV) in hydrous zirconia are similar to those in zirconia (182.2 eV for the binding energy of zirconium), and the weight loss of hydrous zirconia is 21.5%, different from 32.19%, the weight loss of zirconium hydroxide. According to the experimental data, a structure for hydrous zirconia is proposed and then the different phenomena are explained.