An aqueous solution containing divalent iron ions having improved storage stability such that the oxidation over time of divalent iron ions in the aqueous solution containing divalent iron ions to trivalent iron ions is suppressed and the occurrence of the precipitation of iron (III) hydroxide is prevented for long periods. The aqueous solution contains divalent iron ions having improved storage stability characterized in that it contains divalent iron ions and a hydroxylamine salt as a reducing agent and has a pH of 3.0 or lower. The pH is preferably 2.2 or lower and more preferably 1.2 or lower.