The structure of medium carbon and low-alloy steel, commercial pure and (α-β)-titanium alloys, its microhardness, surface roughness, wear and corrosion resistance after anode plasma electrolytic nitriding (PEN) in electrolyte containing ammonia were investigated.     After the PEN of medium carbon steel (0.45% C) the surface steel structure comprises a porous oxide layer (include FeO and Fe3O4 oxides) and a diffusion layer with an increased concentration of nitrogen (include martensite, retained austenite, ferrite, and Fe4N and Fe2-3N nitrides). The nitrogen diffusion decreases the austenitization temperature and results in the formation of martensite after the sample cooling in the electrolyte. Microhardness distribution on the surface profile is correlated with the phase composition of the modified layers. The maximum value of microhardness (1200 HV) and the greatest depth of the hardened zone are observed after the PEN at 750 °C during 10 min. The surface roughness decrease is observed after 10 min treating only. The PEN could decrease friction coefficient from 0.17 to 0.12 and increase wear resistance of 9 times through lubricant sliding against hardened steel (50 HRC) disk with speed of 0.49 m/s and load of 208.6 N and also decrease the corrosion current density of 6 times in 0.1N Na2SO4.   The PEN hardened low-alloy (0.4% C, 1% Cr) samples consist of an oxide-nitride layer (Fe2–3N and Fe3O4), nitride–martensite (Fe2–3N, martensite) layer and martensite-pearlite one. The highest layer microhardness of 780 HV is reached at a temperature of 650 °C. The surface roughness can be decrease from 1.39 m for untreated sample to 1.07 m for sample nitrided at 650 °C. The temperature rises results in the increase in the roughness probably due to the sample oxidizing in the water vapour. The lowest weight loss of hardened layer under lubricant sliding against hardened steel (50 HRC) disk with speed of 0.49 m/s and load of 208.6 N is about 5.5 mg which is only 1/3 of the bare steel. The greatest wear resistance is reached when the sample hardness is maximal and roughness is minimal. The lowest current density of hardened layer in 0.1N Na2SO4 is observed after PEN at 800 °C owing to the protective effect primarily of the iron oxides and the iron nitride secondarily.   It was shown that PEN of VT22 (α-β)-titanium alloy provides formation TiO2 with rutile structure and nitrogen solid solution in titanium. The anode PEN at 800 C during 5 min results in an increase in microhardness to 520 HV and a decrease in surface roughness by 4 times owing to anode dissolution of titanium.     The PEN at 850 °C during 5 min of commercial pure titanium allowing to obtain the hardened surface layer up to 0.1 mm with microhardness 220 HV are proposed. Surface roughness of samples after their nitriding for 5 min at 800 °C decreases from 1.67 to 0.08 μm. The PEN could decrease friction coefficient from 0.70 to 0.15 and increase wear resistance of 42 times through lubricant sliding against hardened steel (50 HRC) disk with speed of 0.49 m/s and load of 208.6 N. The decrease in the treatment temperature leads to the increase in the friction coefficient and the decrease in the wear resistance.   This work was financially supported by the Russian Science Foundation (Contract No. 15-1310018) to the Nekrasov Kostroma State University.