Abstract: The effect of the Mn/S mass ratio on the high temperature ductility of the low carbon steel under low strain rate was researched. The result of the experiments shows that the Mn/S mass ratio has different effect on the high temperature ductility of steel under different temperatures. The effect can be classified into four categories:(1)1 350~1 400℃, the greater the Mn/S mass ratio is, the poorer the ductility is; (2)1 000~1 350℃,the Wn/S mass ratio has no effect on the duchlity; (3)800~1 000℃, the greater the ratio of the Mn versus S is,the better the ductility is; (4)600~800℃, the greater the mass ratio of the Mn versus S is, the poorer the ductility is. The mechanism of the effect of the Mn/S mass ratio on the high-temperature ductility is also analyzed.