The hot ductility of Fe-36Ni invar alloy was studied by a Gleeble-3800 thermal-mechanical simulator and a microcomputer control universal material testing machine. The results show that the alloy has a good hot ductility (RA above 70%) at 1050~1200 °C, which illustrates that the alloy might be suitable for the rolling provided the finish rolling temperature does not go below 1050 °C. Dynamic recrystallization occurred and was found to be responsible for the better hot ductility. However, the alloy exhibits a hot ductility drop (RA below 50%) at 800~1000 °C, which is mainly attributed to the presence of the grain boundary sliding. Serious subscales, which had a typical substructure of the intragranular subscale and the intergranular subscale, occurred in the matrix after oxidation. The compression test indicates that the intergranular subscale will lead to the cracks and significantly deteriorate the hot ductility during deformation process.