Paper examines the effects of ultrasonic impact treatment on the surface hardening of the Ti–6Al–4V (ВТ6) alloy samples obtained by the standard technology and printed by the additive technology ‘xBeam 3D Metal Printing’. To determine the optimal level of the load on the indenter for the microhardness measurements this level is estimated by changing the load in the range of 25–200 g. Orientation dependences of the microhardness of the 3D-printed Ti–6Al–4V (ВТ6) alloy have a slight spread of values ($\pm$ 0,2 GPa). The changes in microhardness of both types of samples are investigated and analysed depending on the duration of ultrasonic impact treatment in the argon stream. The increase in the ultrasonic impact treatment induced hardening effect of the 3D-Ti–6Al–4V (ВТ6) sample as compared to the annealed Ti–6Al–4V (ВТ6) sample can be explained by the change in the structural state, compressive residual stresses, as well as strain induced mechano-chemical oxidation of the surface. The difference in the strength, hardness and plasticity of the near-surface layers leads to a change in mechanical behaviour, which gives the potential for further improvement of the protective characteristics. Hardness measurements can be used to predict the strength of 3D-Ti–6Al–4V (ВТ6) depending on the type of additive manufacturing technology and on the usually required subsequent mechanical or heat treatment.