The microstructural evolution and creep behavior of aged 2.5Al alumina-forming austenitic (AFA) steel were investigated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The average particle size, volume fraction of precipitates and dislocation density were statistically measured to evaluate the contribution of precipitation strengthening and dislocation strengthening to the creep strength. The results suggested that the phase boundaries between Laves and B2–NiAl were incoherent interface, and both B2–NiAl and Laves were main strengthened phases in aged 2.5Al-AFA steel. The creep results indicated that the sample aged for 1000 h exhibited creep capability with the smallest creep strain and steady-state creep rate. The isothermal aging treatment can be considered as an effective way to improve the creep strength of 2.5Al-AFA steel.