Abstract: The influence of strain rate on the hot ductility of two kinds of cast austenitic stainless steels, Cr15Mn9Cu2NiN and Cr17Mn6Ni4Cu2N, has been studied in high temperature tensile tests. Results show that the microstructure of Cr15Mn9Cu2NiN steel was fully austenite, but residual δ ferrites distributed in the boundaries and inside of austenite grains in Cr17Mn6Ni4Cu2N steel. There was little influence on the hot ductility of Cr15Mn9Cu2NiN steel as increasing strain rate from 0.1 s-1 to 10 s-1, because the increased stress concentration on grain boundary was eliminated by the reducing of grain boundary sliding when increasing the strain rate. In the microstructure of Cr17Mn6Ni4Cu2N steel there was lots of interface between austenite and ferrite phase which generated dislocations as the materials deformed at higher strain rate, improving the strength of austenite and ferrite, then decreasing the stress concentration on ferrite, so the reduction of area was increased by more than 10%.