Two　kinds　of　Fe-18Ni-12Cr-based　alumina-forming　austenitic　(AFA)　steels　with　ultralow　carbon　content　were　prepared　by　vacuum　induction　melting.　Creep　rupture　tests　were　carried　out　with　the　applied　stress　range　between　80　and　180　MPa　at　the　target　application　temperature　of　700　degrees　C.　Microstructure　evolution　was　characterized　using　glancing　X-ray　diffraction,　scanning　electron　microscopy　equipped　with　a　detector　of　electron　backscatter　diffraction　and　transmission　electron　microscope.　Compared　with　18-12-Al,　18-12-AlNb　exhibited　superior　creep　properties　including　ten　times　longer　creep　rupture　life　(t(rup))　and　one　magnitude　smaller　minimum　creep　rate　((epsilon)　over　dot(min)).　For　example,　the　(epsilon)　over　dot(min)　at　the　applied　stress　of　140　MPa　was　4.4　x　10(-5)　and　2.1　x　10(-4)　h(-1)　for　18-12-AlNb　and　18-12-Al,　respectively.　The　strengthening　effect　of　B2-NiAl　would　weaken　at　700　degrees　C　due　to　its　ductile-to-brittle　transition.　The　addition　of　Nb　not　only　promoted　the　formation　of　Laves-Fe-2(Mo,Nb),　but　also　resulted　in　formation　of　nanoscale　NbC.　The　GB　Laves-Fe-2(Mo,Nb)　did　not　impair　the　creep　ductility　by　strengthening　GBs,　and　all　the　creep　ruptured　AFA　steels　exhibited　typical　ductile　fracture　mode.　The　GB　Laves-Fe-2(Mo,Nb)　and　NbC　precipitates　contributed　to　the　superior　creep　resistance　of　18-12-AlNb.