Almost all ductile metals and alloys have a ductility minimum in the intermediate temperature range at about from 0.5 to 0.8 melt point, with an intergranular fracture mode l (intermediate temperature brittleness, ITB, or intermediate temperature ductility minimum, ITDM). That was found in Ni-based alloys, Fe-based alloys, Co-based alloys, Ti-based alloys, intermetallic compounds and Al-Mg alloys. One of the problems specific to the continuous casting of steels is transverse cracking, which is induced by the ITB of steel, called as hot ductility. The mechanisms suggested are mostly related to the especial properties such as ferrite mechanism for steels and precipitates mechanism at grain-boundaries. It is clear that the ferrite mechanism cannot clarify the ITB of austenitic steels and the precipitates mechanism cannot clarify that of metals and alloys which have no precipitates at grain-boundaries. In this work, based on the prior works for single-phase and phase transition alloys, the mechanism of hot-ductility for 2.25Cr1Mo alloy was analyzed by using Gleeble machine and Auger spectroscopy (AES). The results show the ductility minimum near 850 ℃ corresponds to the maximum concentration of the impurity sulfur at grain boundaries. And the hot ductility of 2.25Cr1Mo alloy can be explained reasonably by non-equilibrium grain-boundary segregation of sulfur.