This research is devoted to the investigation comparison of effect of SPS (spark plasma sintering) and conventional sintering for the mullite-ZrO2 ceramics development. Mullite-ZrO2 ceramics were produced from different time ball-milled powders. The effect of illite nanoparticles on the powder sintering promotion process was investigated and evaluated. The density and compressive strength as well as microstructure and crystalline phase development of ceramics were investigated in order to show the impact of SPS by comparing with conventional sintering. It is shown that SPS at 1250 °C produces samples with densities that are to 1.6 – 2.2 times higher than densities of samples obtained with conventional sintering at 1300 °C. Both compressive strength and Vicker's microhardness increase correlate well with the increase of density. The microstructure of the SPS samples is dense and consists of well-textured mullite and cubic ZrO2 particles, but conventionally sintered samples form mullite-corundum crystals with tetragonal ZrO2 inclusion. It is shown that illite clay additive is effective to increase density and compressive strength only when using conventional sintering.