Abstract: The dynamic recrystallization and austenite grain size after recrystallization in a new Mn-Cr gear steel were studied at a strain up to 0.7, at a range of temperature from 850 to 1 150°C , at strain rate from 0.1 to 1 s^-1 and at initial austenite grain size from 70 to 150 μm using a Gleeble 1500 thermomechanical test system. The experimental results show that strain rate, deformation temperature and initial austenite grain size are three factors with strong effects on the dynamic recrystallization. Dynamic recrystallization takes place if deformation condition Z is less than the critical value of Zc. The mean dynamically recrystallized grain size (D) is determined only by deformation condition Z and does not depend on the initial austenite grain size. D decreases with increase of Z. The equation of Z=AD^-3.91 was derived to show the relationship between D and Z.