Abstract In this study, the density, compression and mechanical properties of Si3N4-SiO2 composite with different ratios of 0, 3, 5 and 7 wt.% Eu2O3 and 10 wt.% SiO2 as additive were stdudied. Production of composite ceramics in this study was first done by preparing the powder using mixing and milling for 12 h, then forming by cold pressing method and cold isostatic pressing method and finally sintering by spark plasma sintering process. The samples were incubated at 1750 °C for 15 min at a heating rate of 100 °C / min and a pressure of 40 MPa at maximum temperature under vacuum atmosphere. After the grinding process, the particle size of the initial powder mixture was reduced by about 19 %. The results show that after the cold isostatic pressing process, the relative density of the samples increased by 14.67 %. The high amount of beta phase of silicon nitridein the 7%Eu2O3 sample indicates the sufficient amount of liquid phase during the sintering process and the improvement of the dissolution, diffusion and precipitation mechanism, and finally increase the rate of phase transformation of alpha to beta. The highest hardness of 21.61 GPa was observed in 5% Eu2O3 sample, which indicates high density, advancement of dissolution-diffusion mechanism and deposition of nitride compounds in sintering process. Eu2O3 sample due to the presence of glass phase with it can show a amount of toughness 6.1 MPa.m1/2compared to other samples.