Provided are a method and an apparatus for sterilizing a sleeve that can shorten a sterilization process for a paper container sleeve and ensure a sterilization effect. In a method for sterilizing a sleeve in an aseptic filling system that molds the sleeve into a paper container having a bottomed tubular shape by closing surfaces of an open end part of the sleeve and performs sterilization, filling and sealing of the paper container, the sleeve being a tubular body having walls formed by laminating at least paper, in a state where the sleeve stands in a columnar shape, heated air containing a sterilizer is blasted to an inner surface of the sleeve that is to form a bottom part of the paper container to perform sterilization of the inner surface of the bottom part and heating for the closing at the same time.
