In this work, the effect of Al ternary alloy addition on Ni-Ti alloys has been investigated. It has been seen that, with Al addition, martensite transformation temperatures decrease at different rates in Ti-rich and Ni-rich alloys. The paraequilibrium temperature, T₀, and the chemical driving force for martensitic transformation in Ti-rich alloys is independent of Al composition but it increases with Al content in Ni-rich alloys. On the other hand, T₀ and the chemical driving force for R phase transformation are same in Ni and Ti-rich alloys. The results show that Al and Ni contribute equally to the driving force, while Ti contributes the least. It also appears that the interaction of Al with Ti on Ti sites is higher than the interaction of Al and Ni on Ni sites. The variation of lattice parameter of B2 phase in alloys from both the series decreases with Al content, the trend suggesting that Al substitutes both Ni and Ti sites in the B2 lattice.