The effect of a complex hardening treatment consisting of a preliminary electron-beam irradiation and subsequent thermal oxidation on the microstructure, hardness, and wear resistance of Ti-6Al-4V titanium alloy parts fabricated by additive manufacturing has been studied. It was shown that the electron beam treatment of the Ti-6Al- 4V samples gave rise to significant increase of surface roughness. The electron-beam treatment ensured decreasing both the size of primary beta grains and α' martensitic lamellae. This structure was characterized by the presence of extended grain boundaries and high density of dislocations. The observed microstructure modification that took place at the electron beam irradiation resulted in increasing the surface layer hardness up to 8 GPa. Thermal air oxidation of the as-built SLM Ti-6Al-4V samples gave rise to the formation of a thin, high-strength oxide surface layer 3 μm thick. The latter ensured the significant increase of their wear resistance. A more pronounced increase in the surface layer hardness as well as the depth of the oxidized layer, and as a result, the wear resistance of the SLM Ti-6Al-4V samples occurred at employing the combined treatment by the proposed regime.