A nondestructive evaluating method for aged deterioration in austenitic stainless steel comprises an information obtaining step for previously obtaining a relationship between an applied stress σ and the first ratio Ms/χH* between a saturation magnetization Ms and a pseudo susceptibility χH* based on reference minor hysteresis loops obtained by applying stresses σ, respectively, correspondingly to a result of a tensile test for the same kind of material as an evaluation target. In a measuring step, values of the first ratio Ms/χH* are obtained as measured values from measured minor hysteresis loops obtained by measuring the evaluation target. In an evaluating step, the relationship between the applied stress σ and the first ratio Ms/χH* is compared with the measured values, thereby evaluating aged deterioration of the evaluation target. The minor loops are obtained by stepwise changing a magnetic field amplitude Ha within a range of a magnetic field intensity lower than a saturation magnetization.