Plasma electrolysis treatment of metals and alloys by diffusive saturation with light elements provides possibility to improve significantly their operation properties. Anodic plasma electrolysis carburization (PEC) of low carbon steels during several minutes makes it possible to significantly increase the wear resistance and hardness of workpieces [1]. However, it is known that a dense oxide layer is formed on the metal surface after PEC [2]. Purpose of this paper is to determine the effect of surface oxidation on the corrosion properties of workpiece after PEC. Cylindrical samples of steels 20 with a diameter 12 mm and length 10 mm were carburized. The electrolyte are prepared with distilled water, in witch are dissolved ammonium chloride (10%) and glycerol (10%). PEC was carried out in cylindrical working chamber with the longitudinal flow around the sample. Duration of the PEC was 5 min at different temperatures (from 650 to 950 °С). After saturation all samples were cooled in the electrolyte or in the air. Corrosion measurements were carried out using potentiostat ICP-Pro M with three-electrode cell. Carbon was used as the counter electrode and silver-chloride as reference electrode. Tested samples was covered by varnish, the surface area exposed to the electrolyte was 0.4 cm2. The corrosion behavior of the samples was evaluated at 26±2 °С using 0.1 M Na2SO4 solution. The Tafel polarization curves for the samples were recorded at a scan rate 10 mV/s. It was found that the experimental curves is not sufficiently extended linear segments, which can be approximated by the Tafel equation for determining the corrosion current density by the method of Evans diagrams. In this case, corrosion current density can be determined using the equation of the polarization curve as follows [3]:formulawhere j is current density, n is number of electrons involved in the discharge stage, F is Faraday constant, ϕ is potential, R is universal gas constant, T is temperature, jcorr is corrosion current density, α is coefficient, ϕ c orr is corrosion potential. Dependence of the left side (2) on the potential difference ϕ – ϕ corr is linear; therefore the corrosion current density can be estimate by experimental data. It is necessary to select the range of ϕ – ϕ corr is equal to ±(20–50) mV, then extrapolation to the point jcorr (where ϕ– ϕ corr =0) allow us to obtain ln jcorr. Results are shown in the table.tableThese data indicate a stronger tendency to passivation of the samples cooled in air. The results confirm the positive effect of additional cooling in the air on the corrosion resistance.