Zircon, having excellent thermal, chemical, and mechanical properties, is utilized in refractory materials, electronic materials, chemical machines, structural materials, etc. However, zircon generally shows thermal dissociation to zirconia(ZrO2) and silica(SiO2) around the sintering temperature of 1540 oC, and when zircon particles are small and impurities are present, thermal dissociation is known to occur at around 1100 oC. This reduces the mechanical properties of ZrSiO4. In this research, the effect of adding SiO2 and 3Y-TZP to ZrSiO4 has been studied in order to suppress dissociation and improve the mechanical properties. Addition of SiO2 suppressed the dissociation of ZrSiO4 at lower temperatures. It also enabled optimum packing between the particles, resulting in a dense microstructure and good mechanical properties. When 3Y-TZP was added, recombination with the dissociated SiO2 resulted in good mechanical properties by suppressing the generation of pores and the densification of the microstructure.