In this study, the microstructure and surface properties of a low-alloy steel (AISI 4140) treated with pulsed plasma were investigated. Three different plasma-gun nozzle distances of (60, 70 and 80) mm and one battery capacity were chosen for a surface modification. The modified surface layers were examined using a light microscope and X-ray analyses were carried out for all the samples. The X-ray diffraction confirmed a development of new phases after the surface treatment. The samples were subjected to micro-hardness measurements and it was found that the hardness values of the modified surfaces were four times higher than those of the untreated samples. The samples were immersed into liquid nitrogen and then broken in a Charpy machine. The fractured surfaces were exposed to SEM and EDS analyses. At the end of the study, thin grains originating from the consumable electrode were detected. After the pulsed-plasma treatment, new structures were obtained.