Abstract: A method for sterilizing an artificial organ with high pressure steam in an autoclave which comprises passing a sterilized high temperature liquid maintained at a temperature sufficient for the sterilization through the artificial organ, thereby raising the inner temperature of the artificial organ approximately to a sterilization temperature, heating the artificial organ externally to a sterilizing temperature and maintaining that temperature for a predetermined time to sterilize the artificial organ, and passing a sterilized low temperature liquid through the artificial organ to cool it from the inside thereof, while cooling the artificial organ from the outside thereof. The sterilized low temperature liquid is one sterilized thermally followed by cooling, and in a preferable embodiment, the sterilized high temperature liquid is cooled and then introduced into the artificial organ.