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An alkaline precipitation method was introduced to produce hydrous cerium oxides. The prepared powder was characterized by Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, and high temperature treatment. Adsorption capacity of different temperature treated hydrous cerium oxides does not directly correlate with BET specific surface area. Phosphate adsorption isotherms follow the Langmuir equation below the treatment temperature of 800℃. Phosphate adsorption causes no change on the structure of a hydrous cerium oxides, and no signs of CePO4 precipitates are found. The ion-exchanging structure of hydrous cerium oxide plays a fundamental role in phosphate adsorption. The structure is highly temperature resistant and forms adsorption sites which adsorb both water and some anions. Complete loss of adsorption ability cannot be achieved unless the treatment temperature is higher than 1200℃. Mechanism study shows that the adsorption of phosphates is mainly an anion-exchange process.