A sterilizing container having a lid with an outer flange which cooperates with the upper edge of a base and a resilient member for sealing the container. The lid contains a mechanism for automatically moving the lid into sealing engagement with the base. Located on both the outer flange of the lid and the upper edge of the base are locking means which interact to place the lid in a sealing engagement with the base when the lid is moved by the moving mechanism on the lid. The container is designed to receive articles such as medical instruments which are sterilized when the container is placed in an autoclave, subjecting the instruments or articles to a sterilizing environment. The moving mechanism on the lid includes means responsive to the sterilizing environment to automatically bring the lid into sealing contact with the base prior to the return of the surrounding environment to ambient conditions, preserving the sterilized instruments until needed for use.