Abstract: The hot ductility behaviors of Fe-36Ni alloy in the temperature range of 900-1200 ℃ were investigated by using a Gleeble-3800 thermal simulator. The influence factors and mechanism of action on the hot ductility were systematically analyzed by FaetSage software, scanning electron microscopy and transmission electron microscopy. The results show that inclusions in the investigated alloy are mainly Al₂O₃ + Ti₃O₅ + MnS, and most inclusion sizes are below 0.5 μm. The hot ductility of the alloy in the temperature range of 900-1050 ℃ is influenced by grain boundary sliding and dynamic recrystallization. Nano-scale size (<200 nm) inclusions at grain boundaries effectively inhibit the occurrence of dynamic recrystallization as a result of the pinning effect and decrease the grain boundary cohesion. Moreover, micro-scale size (>200 nm) inclusions at grain boundaries promote the nucleation and propagation of cracks during grain boundary sliding and decrease the hot ductility of the alloy. Increasing the temperature makes the driving force for dynamic reerystallization larger than the pinning effect, and thus increases the hot ductility significantly by the occurrence of dynamic recrystallization when the temperature exceeds 1050 ℃. In the temperature range of 1100-1200 ℃, the formation of interdendritic cracks, the coarsening of recrystallized grains and the enhanced grain boundary sliding deteriorate the hot ductility of the alloy.