Abstract: Homogenous coprecipitation of Ce3+，Y3+ was performed to prepare (Ce0.8Y0.2)2(C2O4)3 solid solution，by using diethyl oxalate，cerium nitrate and yttrium nitrate as starting materials，and urea as pH adjuster. The co-precipitates produced under different conditions were analyzed by TG-DTA and the result indicated that the co-precipitates （n=0～35.5，n：mole ratio of urea to diethyl oxalate） produced were oxalate solid solution. From SEM observation its particle average size decreased from 10μm to 0.5μm with increasing n from 0 to 35.5. The oxides derived from the oxalate solid solutions were confirmed to be Y-doped CeO2 by XRD analysis and lattice constant calculation. Its crystallite size is about 10nm.