To improve the storage stability of cereals economically in no need of methyl bromide by allowing air or an inert gas containing chlorine dioxide to stay in or pass through the cereal grains held in a tightly closed vessel.

Chlorine dioxide or the air or an inert gas containing chlorine dioxide is retained in or passed through the cereal grains stored in a tightly sealed vessel. In a preferred embodiment, the concentration of chloride dioxide in the air or the inert gas containing chlorine dioxide is set to 10-500 ppm and the air or the inert gas is allowed to stay in the cereal grains for 10-240 minutes.