Deformation microstructures of the gamma-TiAl Phase in two-phase (alpha(2) + gamma) alloy, Ti-46Al-2V-0.4Er (all compositions are given in atomic percent), have been studied by transmission electron microscopy. Heat treated samples of this alloy were subjected to 3% plastic strain in compression at room temperature, 600 degrees C, and 900 degrees C. Majority of dislocations present in the as heat treated and deformed samples are of b = 1/2 < 110] type. Formation of loops from the dislocations are also observed. Isolated super dislocations and faulted dipoles are seldom seen in the microstructures. Plenty of twins are present in these samples and it appears that their density increases with increasing deformation temperature. The deformation microstructures of the alloy studied here are quite similar to those in the binary two-phase titanium aluminides or the V containing two-phase titanium aluminides. It appears that Er does not significantly change the deformation microstructure of this two-phase alloy, although Er has a significant effect on the deformation microstructure of the single-phase gamma-TiAl alloys.