Abstract: To investigate the effect of residual elements Cu, As and Sn on the hot ductility of steels, the hot ductility of low alloy steel continuous casting slabs containing some Cu, As and Sn was measured by tensile tests with a Gleeble-1500 tensile test machine. It is found that the low ductility region Ⅲ is between 920 and 730℃. Embrittlement in the region Ⅲ is caused by Cu, As and Sn segregation along the austenite intergranular in the austenite single-phase low-temperature range, which weakens the binding energy of the intergranular and induces brittle fracture along the intergranular; the precipitation of proeutectoid ferrite film along the austenite intergranular in the austenite and ferrite two-phases range induces intergranular cracks. Cu, As and Sn in the steel increase the width and depth of the low ductility region In and enhance its upper limit critical temperature.