High-energy ball milling process has been applied to gadolinia-doped ceria system. The sinterability of gadolinia-doped ceria was significantly enhanced by the high-energy ball milling process. A comparison was also made of the sintering behavior of milled powders doped with gallia as a sintering aid. Dense Ce0.8Gd0.2O1.9 ceramics with 97% of the theoretical density could be obtained by sintering the milled mixture with 0.5 mol% Ga2O3 addition at 1,250 degrees C for 5 h.