Fe3Al nano-particles and commercial purity Al2O3 powders were used as raw materials to fabricate in situ reinforced Al2O3/Fe3Al nano/micro-composites. Densification and microstructure were studied. The Al2O3 matrix grains were characterized by platelet grains. The Fe3Al particles inhibited the grain growth of Al2O3 grains and limited the densification of the composites. In Al2O3/Fe3Al composites, the Fe3Al particles were uniformly dispersed in the Al2O3 matrix. The major Fe3Al micro-particles, about 1 mm in average size, existed at Al2O3 grain boundaries, and the Fe3Al nano-particles were found embedded in the matrix grains. The grain size of the intragranular particles ranged from several to several hundred nanometers. The grain size and aspect ratio of Al2O3 platelet grains and distribution of intragranular Fe3Al could be optimized by controlling the Fe3Al contents and sintering process. The in situ formed Al2O3 platelet grains, as well as Fe3Al dispersoids, were beneficial to the increase of the mechanical properties of alumina.