Alloys of Ti-40wt%Al, Ti-43wt%Al and Ti-48wt%Al were nitrided at a temperature of 1000-1300 K for 3.6x10⁵ s. Hardness and thickness of the nitride layers on the alloys were determined. It was found that the values increased with increasing nitridation temperature and aluminium concentration in the alloys. The nitridation depth and the mass increase per unit surface area were in the form of the Arrhenius equation. The mechanism of the nitridation process is explained in relation to the nitridation depth and hardness. Additionally, the results from XRD analysis showed consistency with the mechanism of the nitridation process.