Aluminium titanate (Al2TiO5) with an excellent thermal shock resistant and a low thermal expansion coefficient was obtained by solid solution with MgO, SiO2, and ZrO2 in the Al2TiO5 lattice or in the grain boundary solution through electrofusion in an are furnace. However, these materials have lw mechanical strength due to the presence of microsracks developed by a large diffierence in thermal expansion coefficients along crystallogtaphic axes. Pure Al2TiO5 tends to decompose into α-Al2O3 and TiO2-rutile in the temperature range of 750~1300℃ that render it apparently useless for industrial applications. Several thermal shock rests were performed: Long term thermal annealing test at 1100℃ for 100 hrs; Cycic thermal shock in a two chamber furnace between 750 and 1400 ℃ for 100 h; and water quenching from 950℃ to room temperature(RT). Cyclic thermal expansion coefficients up to 1500℃ before and after decomposition test was also measured using a dilatometer. Changes in the microstructure, thermal expansion coeffivients, Young's modulus and strengths were determined. The role of microcracks in relation to thermal shock resistance and thermal expansion cofficient is discussed.