Two 0.17C-3Mn-1.5Al-0.2Si-0.2Mo steels with and without Nb microaddition were melted in a vacuum induction furnace. The steels are characterized by bainitic-martensitic structures with large fraction of retained austenite. To design a thermomechanical treatment for steels with required multiphase structures a knowledge of their hot deformation resistance and softening kinetics is of primary importance. The paper presents the results of the compression tests carried out at various temperatures and strain rates using the Gleeble simulator. A softening kinetics was determined in a double-hit compression test. It was found that the dynamic recrystallization was a process controlling work hardening of steels except for hot deformation conditions characterized by the highest Zener-Hollomon parameter values. Nb microalloyed steel has higher flow stresses and peak strains than the steel without Nb. A solute drag effect of niobium results also in a slower recrystallization kinetics for the Nb containing steel.