The paper presents the evaluation of hot deformability of two types of structural steel grades, (0.25C-1Mn-0.25Si-CrNiMo and 0.75C-1Mn-0.25Si), in the process of continuous and intermittent compression of samples. Tests were conducted in Gleeble 3800 thermo-mechanical simulator, on axisymmetric specimens with diameter of 10 mm and the length of 12 mm. Continuous compression tests were performed in the temperature range from 900°C to 1100°C, at a rate of 0.3 s-1 and 3 s-1, while intermittent tests, consisting of four-stage plastic deformation – simulating successive rolling passes, were done in the temperature range from 850°C to 1000°C, applying the same rates. Conducted research allowed determining the flow curves and identifying the thermally activated mechanisms that determine the strengthening under given conditions of temperature and strain rate. Regardless of the applied strain rate, higher values of yield stress were noted for 0.25C-1Mn-0.25Si-CrNiMo steel. Microstructures of the examined steels, obtained after cooling the samples from the compression finish temperature, fully correlate with obtained hardness results. Hardness of specimens, obtained from the 0.25C-1Mn-0.25Si-CrNiMo steel grade, cooled in compressed air from the plastic deformation finish temperature (from 900°C to 1100°C), ranges from approx. 517 HV1 to about 431 HV1, while hardness of the 0.75C-1Mn-0.25Si steel samples, produced under the same conditions, ranges from approx. 806 HV1 to about 683 HV1. As part of the work, CCT (Continuous Cooling Transformation) diagrams of the analyzed steels were also calculated, using an original author’s program based on artificial neural networks.