The invention relates to a fractional vacuum sterilization method for objects such as blood tubing systems or cassette systems, which are sterilized in outer packagings. The spatial extent of the outer packaging during the evacuation step is minimized here by inserting a packing into the sterilization chamber and thereby achieving an efficient gas exchange through the gas-permeable outer packaging. The number of vacuum-pressure cycles required to establish a saturated sterilization medium atmosphere in the outer packaging and in the object to be sterilized is thereby reduced.