The possibility for increasing the mechanical properties of the 20 GL steel by electric-spark alloying (ESA) using nickel or molybdenum electrodes and by the multifactor positive influence of surface finishing by means of ultrasonic impact treatment (UIT) is demonstrated. The separately applied UIT leads to increase in microhardness and fatigue strength of the 20 GL steel on the base of 10$^{6}$ cycles under amplitude of cyclic loads ranged within 360–400 MPa. The surface layer after ESA with molybdenum shows twice-higher microhardness than those of the original and nickel-alloyed steel samples that is due to the solid-solution hardening and multiphase state of the molybdenum-modified layer. The finishing UIT applied to the ESA-modified layers increases the fatigue durability of the 20 GL steel because of the roughness reduction (lowering the superficial stress raisers), the formation of residual compressive macrostresses, and the creation of dislocation-cell structures (increasing the number of microstructural stress raisers). Both factors lead to the reduction in probability of both the strain localization and the early nucleation of fatigue cracks.