Nanocrystalline structure with the grain size range 16 – 40 nm were formed on 65G steel’s surface due to variation of treatment regime of mechanical-pulse treatment, which is used for surface nanostucturization and strengthening mainly structural steels due to severe plastic deformation based on high-speed friction. It was demonstrated that variation of treatment regimes, namely, tool and specimen rotating velocity Vt and Vs, longitudinal feed of the strengthened tool relative to the specimen S and depth of impression of the strengthened tool to the treated component t ensured different pressure, and, respectively, the temperature in the friction contact zone, consequently, provided obtaining of strengthened surface nanocrsytalline layer of different thickness, microhardness, and grain size in it. Therefore, it received the thickness of surface strengthened layer varied from 96 to 163 μm, the surface microhardness increased from 7.7 to 9.8 GPa accordingly. Based on carried out researches, the following main regularities were determined: (i) increment of the specimen rotating velocity resulted in raising the grain size and decreasing the thickness of the layer (ii) due to raising of the pressure in the friction contact zone, the grain size decreased and the thickness of the layer increased; (iii) due to raising of the longitudinal feed of the tool relative to the specimen the grain size slightly decreased and the thickness of the layer slightly raised. It was also established that increment of the thickness of strengthened layer and decreasing its grain size led to increasing of contact fatigue (number of cycles before destruction) of treated steel.