The hot ductility of Fe-36 Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850- 1 050 ℃,and the improvement mechanism of the hot ductility was analyzed using a combination of SEM,EDS,and OM. The results indicated that Fe-36 Ni invar alloy exhibited poor hot ductility below 1 050 ℃,which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However,the alloys with cerium contents of 0. 016% and 0. 024% both demonstrated substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0. 016% cerium at 950 ℃ and the alloy with 0. 024% cerium at 900℃ was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined the grain structure.The occurrence and acceleration of dynamic recrystallization were found to be responsible for the high hot ductility of the alloy with 0. 016% cerium at 1 000 ℃ and the alloy with 0. 024% cerium at 950- 1 000 ℃ as a result of the refinement of the grain structure by addition of cerium. The hot ductility of Fe-36 Ni invar alloy with different additions of the element cerium was investigated using a Gleeble-3800 thermal-mechanical simulator over the temperature range 850-10000C, and the improvement mechanism of the hot ductility was analyzed using a combination of SEM, EDS, and OM. The results indicated that Fe-36 Ni invar alloy showed poor hot ductility below 1 050 ° C, which was mainly attributed to weak grain boundaries and the action of grain boundary sliding. However, the alloys with cerium 016% and 0. 024% Both the substantial improvement in the hot ductility over the entire testing temperature range. The observed improvement of the hot ductility of the alloy with 0. 016% cerium at 950 ℃ and the alloy with 0 024% cerium at 900 ℃ was associated mainly with the grain boundary strengthening and the restriction of the grain boundary sliding because the addition of cerium reduced the segregation of sulfur at grain boundaries and refined t he grain structure. The occurrence and acceleration of dynamic recrystallization were found to be responsible for the high hot ductility of the alloy with 0. 016% cerium at 1 000 ° C and the alloy with 0. 024% cerium at 950-1000 ° C as a result of the refinement of the grain structure by addition of cerium.