The microstructural evolution during sintering of Al2O3 was investigated to determine the role of Al nanoparticles. Compared with specimens without Al,a few platelike Al2O3 grains were observed with the addition of 0.01% and 0.1% (mass fraction) Al nanoparticles. When Al content was increased to 0.5%,a fine,equiaxed and homogeneous grained microstructure was obtained. This effect of Al on the microstructure of the sintered Al2O3 is similar to that of MgO.