The synthesis of AlN and TiB 2 by spark plasma sintering (SPS) and the effect of Nb 2O 5, Y 2O 3 and ZrO 2 additions on the mechanical properties and densification of the produced composites is reported and discussed. After the SPS process, dense AlN and TiB 2 composites with Nb 2O 5, Y 2O 3 and ZrO 2 were successfully prepared. X-ray diffraction analysis showed that in the AlN composites, the addition of Nb 2O 5 gives rise to Nb 4N 3 during sintering. The compound Y 3Al 5O 12 (YAG) was observed as precipitate in the sample with Y 2O 3. X-ray diffraction analysis of the TiB 2 composites showed TiB 2 as a single phase in these materials. The maximum Vickers and toughness values were 14.19 ± 1.43 GPa and 27.52 ± 1.75 GPa for the AlN and TiB 2 composites, respectively.