The effect of aging in air at 650℃ for 100~1000 h on the tensile properties of superaustenitic stainless steel in the range RT-750℃ and the fatigue crack growth behaviour at RT and 650℃ was studied. Yield strength and ultimate tensile strength were almost the same between the as-received and the aged specimen. The frac­ture strain, however, decreased significantly from aging, and the fracture surface of the aged specimen at RT test was intergranular. The fatigue crack growth rate at RT is enhanced by aging at the high stress in­tensity factor range. This is due to the occurrence of an intergranular fracture in the aged specimen. At 650℃ the fatigue crack growth behaviour of both the as-received and the aged specimen was almost same with no intergranular fracture.