  Stainless steel is a candidate of the inner surface of the storage container
for LAB-based Gadolinium loaded liquid scintillator (Gd-LS) to be used in the
JSNS$^2$ neutrino detector. Aging effect on Gd concentration of Gd-LS was
investigated with the Gd-LS sample stored in the passivated stainless steel
bottle in two independent methods. The direct comparison of the neutron capture
time measurement showed that there is no significant degradation of the capture
time after 602 days aging. Titration was performed to measure Gd concentration,
and the result after 466 days aging is consistent with the result before aging
within the uncertainty of the measurement. The upper limit of degradation of Gd
concentration in 21 kL tank case is estimated as 0.5 % for 10 years of storage.
Both results lead to a conclusion that stainless steel is usable for Gd-LS
storage for JSNS$^2$ experiment.
