We investigated the composition dependence of the tunneling magnetoresistance (TMR) behavior and the stability of the magnetic tunnel junctions (MTJs) with TiAlOx barrier and the microstructural evolution of TiAl alloy films. The TMR ratio increased up to $49\%$ at $5.33;at\%$ Ti. In addition, a significant tunneling magnetoresistance (TMR) value of $20\%$ was maintained after annealing at $450^{circ}C$, and the breakdown voltage ($V_B$) of and 1.35 V were obtained in the MTJ with $5.33;at\%$ Ti-alloyed AlOx barrier. These results were closely related to the enhanced quality of the barrier material microstructure in the pre-oxidation state. Ti alloying enhanced the barrier/electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal and electrical stability of the MTJs.