Al2TiO5 ceramics of $alpha$-Al2O3 and TiO2 mixture doped with MgO and SiO2 were fabricated by sintering at 150$0^{circ}C$ for 2 h. Sintered bodies were heat-treated at 115$0^{circ}C$ for 24h, XRD was used for the phase analysis and measurement of lattice parameter. It was confirmed that MgO and SiO2 form solid solution with Al2TiO5. Substitutional solid solution is formed by MgO with the formation of 2Al3+longleftarrowMg2++Ti4+ It is though however that Si4+ makes interstitial solid solution with Al2TiO5 rather than substitutional solid solution by considering is XRD results. The suppression of thermal decomposition depends on moderating structural distortion of Al2TiO5 lattice. Even though the same additives were added suppression effects show con-siderable difference with their solid solution mechanisms