Misch metal (Mm), consisting of Ce and La, was added to Ti-45Al-3Mo-2Nb alloys in order to investigate phase transformation and microstructural changes. The pseudo-binary phase diagram was estimated via PANDAT software (TM). The addition of Mm caused a decrease in both the fractions of alpha(2)/gamma lamella and the beta(0) phase, and served as an important factor for a collapse of lamellar structures. In addition, Mm significantly decreased the colony size of the alloy, resulting in an increase in high-temperature tensile yield strength of similar to 40% for the alloys with 0.3 at% Mm at 800 A degrees C. It appears that the addition of Mm affects the phase stability and increase the proportion of the gamma phase. The microstructural changes, with respect to Mm additions, were discussed in terms of structural observations during isothermal heat treatments.