The effect of Mo additions on the microstructure and the room temperature deformation behavior of directionally solidified (DS) and polycrystalline forms of two-phase TiAl alloys were systematically investigated. Tensile elongation as large as 6.5% was observed for a polycrystalline specimen with duplex structure, but it varied with the strain rate and the test environments. In case of the fully lamellar structure, however, tensile elongation lover than 1% was obtained both in polycrystalline and in DS specimens. It was found from directional solidification studies that the lamellar boundary orientation in DS ingot has been affected by the growth rate and Mo contents. In case of Ti-48.5at.%Al-0.6at.%Mo DS ingot grown at a growth rate of 300 ㎜/hr, the lamellar boundary was nearly perpendicular to the growth direction. However, the lamellar boundary orientation of Ti-47.5at.%Al-2.5at.%Mo DS ingot was nearly parallel to the growth direction when the directional solidification was performed at a growth rate of 90 ㎜/hr. These results have shown that solidification procedures of TiAl with a nearly stoichiometric composition has been affected by Mo addition and, therefore, the lamellar boundary orientation in DS ingot could be controlled by changing the growth rate and the content of Mo additions.