Al2O3 nanospheres are employed to synthesize alumina ceramics with uniform grains and superior hardness, and the sintering behaviors of these nanoparticles, including density, grain size and hardness evolution are studied. The results show that the aggregates are avoided during sintering owing to the employment of mono-dispersed spheres. The uniform pores packed by spherical particles can inhibit uneven grain growth effectively, which result in the uniform grains and thus the favorable hardness. The ceramic with 97.6% of theoretical density and 1.1 mu m of average grain size is obtained after sintered at 1550 degrees C, and superior hardness of 23 +/- 1.4 GPa is achieved. Furthermore, the kinetic analysis reveals that surface diffusion is responsible for the mass transport during the initial sintering stage. The higher Ea value than that of irregular powders conforms, on a side-note, the uniform pores are more effective in preventing the merging among grains and are benefit to the homogenization of grains. (C) 2016 Elsevier B.V. All rights reserved.