Well-developed alpha(2)'-martensitic laths were formed in a Ti-40Al-10V (at.%) alloy after a homogenization treatment within the beta phase field followed by brine quenching. The morphology and crystallography of martensite were examined by electron backscatter diffraction. It was found that the martensitic transformation was incomplete and about 35 vol% beta phase was retained to room temperature. No diffusional or massive transformation has been detected in the b grain interior. All the 12 martensite variants were formed according to the Burgers orientation relationship (BOR) with the parent beta grain. While global variant selection has not been detected, local variant selection occurred so that three self-accommodant variants which shared a common h11.0i axis were predominant in local regions. Based on the traces of the variants, the habit plane was determined to be close to {679} beta by using a simply geometrical method. Besides, alpha(2)' plates were frequently observed along the beta grain boundaries, which accorded to a strict BOR with one of the adjacent beta grains, but tended to grow into the other beta grain and hence resulted in serrated interface. Such features were an indication of massive transformation. Moreover, an apparent variant selection criterion for the grain boundary alpha(2)' plates was noted. That is, if a alpha(2)' variant has, in addition to an exact BOR with one of the two adjacent beta grains, a near BOR with the other beta grain, this alpha(2)' plate would be very large and even extends along the entire grain boundary.