PURPOSE: To sterilize a medical instrument and to preserve the sterilized one in an aseptic state by sealing liquid propylene oxide infiltrated in a liquid absorbable material in a container at a temp. of the b.p. thereof or more along with an object to be sterilized and heating the container to gasify propylene oxide to bring the same into contact with the object to be sterilized for a predetermined time.
CONSTITUTION: One surface 3 of an inner bag 1 is formed of a gas permeable material and the whole of an outer bag 6 is formed of a gas impermeable material. In sterilization, propylene oxide 4 infiltrated in a liquid absorbable material is put in the inner bag 1 along with an object 5 to be sterilized to hermetically seal the inner and outer bags and the whole is heated to gasify propylene oxide. After the finish of sterilization, the outer bag is removed and the inner bag is ventilated through the gas permeable material to make it possible to remove remaining propylene oxide.