[en] Studied is the surface microstructure of 5VMTs and Nb-1 Zr niobium alloys after the intensive diffusion saturation with oxygen in the temperature range of 600-900 deg C. The influence of the changes in surface layer structure on the mechanical properties of samples with different cross-sections is investigated. It is established, that the saturation with oxygen at the temperatures of 600 and 900 deg C occurs by means of preferential formation of oxide phase in surface layers, while the temperature of 800 deg C promotes the intensive deep saturation without noticeable phase formation. The principal difference is shown between the character of oxides, formed in work-hardened and recrystallized materials which results in the difference in the mechanical properties of the samples saturated with oxygen