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This work presents the research results of the impact of plasma electrolyte hardening (PEH) on the structure and properties of structural 40HN and 20H2N4A steels. Thermal surface hardening of steel parts is one of the most effective and efficient ways to increase the service life of loaded elements of machines and mechanisms, also to reduce their material consumption. In this case, only the most loaded working surface of the part is strengthened, leaving the core intact. The PEH process was carried out in an electrolyte from an aqueous solution containing 20% ​​sodium carbonate and 10% urea. It has been established that a modified layer after PEH is formed with a thickness of 0.5-0.7 mm which consist of a hardened layer of fine-grained martensite and an intermediate layer of perlite and martensite. Microhardness increases by 2 times, wear resistance increases by 3 times after PEH. The conducted research showed the promise and feasibility of using the developed method to improve the operational properties of parts operating under friction and wear. This method, which consists in heating the part for 2 s, is recommended for hardening gears made of 40HN and 20H2N4A steels without additional heat treatment. PEH ensures the achievement of a technical and economic effect due to the use of simple equipment, not expensive aqueous solutions, reduction of processing time, and also as a result of increased wear resistance and microhardness of steels.