This paper deals with a colloidal processing route that uses alkoxides to obtain alumina nanocomposites. These alkoxides, which include zirconium IV-propoxide, tetraethyl orthosilicate (TEOS), yttrium methoxyethoxide (ABCR, Germany) are used both separately and in different mixtures as coating for alumina particles in non-aqueous media. As a consequence the grain boundaries of the high-purity alumina powder are modified by segregation of the secondary phases or by the formation of well-distributed zirconia, YAG and mullite nanoparticles. The presence of these oxides at the grain boundaries (GBs) drastically affects the evolution of the microstructure, and the properties of the resulting materials. Thus high dense composites with microstructures formed by an alumina matrix and a very homogeneous distribution of secondary nanophases can be obtained.