CZO (CeO2-ZrO2) and CZYO (CeO2-ZrO2-Y2O3) series of mixed oxides were prepared by coprecipitaion, and a part of these oxides were loaded with precious metals (PM). XRD, BET, and oxygen storage capacity (OSC) investigations were performed on samples aged at 750, 900, and 1050 ℃. It was observed that BET surface area and OSC showed a marked decrease in CeO2 aged at high temperature, and the crystallite size showed an obvious increase. The CZO samples consist of cubic- and tetragonal crystal phases, and their crystallite size increase rapidly when aged at high temperature. The CZYO samples consist of single crystal phase when the content of Y exceeds 0.15 mol, and their crystallite size increases slowly during high-temperature aging. It is concluded that additive Y can stabilize the performance of CZYO oxides. In the aged CZO and CZYO mixed-oxide systems, addition of a small amount of precious metals (Pt, Pd, Rh) increased the rate of reduction and led to an obvious improvement in OSC. OSC of CZO and CZYO with precious metals are related to their composition and the type of precious metal.