Results of research of mullite-ZrO2/Y2O3 - SIAlON oxide ceramics, formed from mixtures with the SiAlON nanopowder additive using Spark Plasma Sintering (SPS) and a comparison of the characteristics of adequate ceramics obtained with traditional process, have been reported. It showed that SPS-process results in a significant (when compared to the conventional method) increase of density from 3.10-3.32 g/cm3 and a compressive strength of 295-305 MPa of ceramics, depending on the amount of SiAlON additive. These results are due to a packing density of mullite formations in the microstructure of sintered samples, including the inclusions of cubic ZrO2.