The effect of Zr content on the thermal stability of mechanically alloyed Al-8wt.% (Ti+Zr) alloys was investigated. As the Zr to Ti addition ratio increased the decrease of hardness due to the long time exposure at high temperature reduced so that the thermal stability of the alloy was improved. From the TEM work it was found that the coarsening of precipitates was responsible for the decrease of hardness and the coarsening of precipitates could be suppressed by the addition of Zr, XRD, SAD and EDS analyses confirmed that these precipitates were consisted of DO$sub$22/, and DO$sub$23/ type Al$_3$(Ti+Zr) ternary in termetallic compounds. Especially for the DO$sub$23/ Al$_3$(Ti+Zr), the lattice parameter changed toward the smaller lattice mismatch between the precipitate and Al matrix as the Zr content increased. Therefore, it was considered that the improvement of thermal stability of Al-8wt.% (Ti+Zr) alloys was due to the formation of the ternary Al$_3$( Ti + Zr) intermetallic compounds.