The microstructures and tensile properties of additively manufactured Ti-base alloys were investigated. Ti-6Al-4V and Co-Cr-Mo alloy powders were blended and used for directed energy deposition of bulk samples containing 5 and 10 wt.% Co. The Ti-6Al-4V and 5 wt.% Co samples exhibited an α phase at β grain boundaries, which caused a significant reduction and anisotropy of the tensile ductility. A single-phase β microstructure exhibiting equiaxed grains with a grain size of 36 μm, random texture, and isotropic tensile properties was obtained for the as-deposited 10 wt.% Co sample. These phenomena could be ascribed to the high Co content and the resulting enhanced stability of the β phase and the constitutional supercooling of the melt-pool.