Abstract: A method and a container for long-term storage in a state in which harmful insects do not propagate, in a case in which grains such as unpolished rice or the like are filled and stored. An inner bag (10) made of a flexible material is accommodated in an outer bag (12) which has high-strength. After grains are filled in the inner bag, the inner bag (10) is filled with carbon dioxide gas and is closed. The grains are stored in a state in which harmful insects are exterminated. It is preferable from the standpoint of the insecticidal effect that the inner portion of the inner bag (10) is able to maintain a carbon dioxide gas concentration of 40% or more for 7 days or more. Because the inner bag has the property of a CO.sub.2 permeation amount of less than or equal to 6300 cc/m.sup.2 .multidot.24 hr 1 atm, an oxygen-deficient state can be maintained.