Effects of Zr addition on the phase stability of $L1_{2}$-based Al-Ti-Cr alloys was investigated and moreover in order to improve the thermal stability of Al-21Ti-23Cr, Zr was added to the alloy. As a result of exposing Zr added alloys at 800$^\circ$C for 10 and 100hr, it was found that $L1_{2}$ phase decomposition was repressed by Zr addtion. Considering both mechanical properties and phase stability, 3 at.\% of Zr addition were suitable. As a result of aging Al-21Ti-23Cr and Al-18Ti-23Cr-3Zr at 800$^\circ$C for 100 and 500hr, it was found that $L1_{2}$ phase decomposition was repressed for 500hr by Zr addition. Phase decomposition of $L1_{2}$ phase with aging temperature was investigated. Fraction of $L1_{2}$ phase decomposition was decreased all over the temperatures by Zr addition and besides temperature range of $L1_{2}$ phase decomposition became narrow as Zr addition. In three-point bend tests to investigate the correlation between enhanced phase stability and fracture toughness, Al-18Ti-23Cr-3Zr alloy exhibited better cracking resistance after exposure at 800$^\circ$C than Al-21Ti-23Cr. This demonstrated that improved phase stability resulted in the enhancement of fracture toughness of $L1_{2}$-based alloys. Therefore, in the Al-Ti-Cr system, Zr added $L1_{2}$-based alloys are more appropriate for the application of coating materials when considering phase stability coupled with fracture toughness.
