Abstract: Single compression tests were carried out for Nb-Ti and Nb-Ti-Mo microalloyed steels by using MMS-300 thermal simulation tester. The hot deformation behavior of the steels and the effects of Mo and deformation conditions on dynamic recrystallization had been studied. The dynamic recrystallization activation energy and the models for deformation resistance of the steels were obtained. The results show that the deformation resistance of the tested steel increased with the deformation temperature decreasing (800~1 150 ℃) and strain rate increasing (0.1~10 s-1). Microalloying element Mo addition produced a increase for deformation resistance and recrystallization activation energy, a retardation for dynamic recrystallzation, and the effect of deformation temperature on deformation resistance increased.