The present invention provides a steam sterilizer including a primary container and a secondary container. The primary container includes a primary base. The interior of the primary base is provided with a heating means. The surface of the primary base is covered by a primary box having a downward opening. The secondary container movably covers the top of the primary box. The secondary container includes a secondary base. The surface of the secondary base is covered by a secondary box having a downward opening. The top of the primary box is provided with a primary through-hole for allowing steam to flow through. The bottom of the secondary base is provided with a secondary through-hole corresponding to the primary through-hole. The secondary container is movably disposed on the top of the primary container to share the steam.
