PURPOSE: To obtain a stainless steel alloy composition having resistance to stress corrosion cracking promoted by irradiation, by preparing an austenitic stainless steel alloy composition having a specified compsn. in which each of content of N, B, C, Si, P and S is prescribed.

CONSTITUTION: The austenitic stainless steel alloy composition contg., by weight, ≤0.01% N (totally placed not in boundaries but in the alloy matrix in substance), ≤0.003% B (totally placed not in boundaries but in the alloy matrix in substance), ≤0.01% C, ≤0.02% Si, ≤0.002% P, ≤0.002% S, about 9 to 15% Ni and about 18 to 20% Cr, selectively contg. about ≤0.3% Mo and components trapping N into the matrix (one or more kinds among Ti, Zr, Hf, Ta, Be, Ce, Y, Nb and their mixtures) by effective quantity, and the balance Fe is prepd.