Gadolinia-doped ceria (GDC, Ce0.eGd0.201.9) powder with particle sizes smaller than 10 nm is synthesized via co-precipitation. The effects of powder pre-treatment before sintering on sinterability of the GDC nanopowder are investigated. It is found that low speed, dry milling of the as-synthesized powder leads to enhancements in sinterability for sintering temperatures at 1000, 1100 and 1200°C. As a result, the pellets made from the dry milled powder exhibit the highest densities among all the sintered pellets investigated in this study. In contrast, calcination at 400°C of the as-synthesized powder leads to lower density pellets sintered at 1000 and 1100°C in comparison with those pellets made from the as-synthesized powder and the dry milled powder. The pellets using the dry milled powder sintered at 1200°C reach the density of 94% of the theoretical and contain only isolated micrometer and nanometer pores. As such, these GDC membranes can be used as the electrolyte for solid oxide fuel cell applications because they are impermeable to gaseous fuels and oxidants. The mechanisms for the enhanced sinterability due to dry milling and the decreased sinterability due to calcination are discussed.