Abstract: A container closure for sterilely packing fluids and provided with a neck and a cap lockable thereon, consisting of a cover portion and a skirt portion which are connectible through a single snap closure and in the non-connected condition are surrounded by a protective cap which prevents undesirable connection of cover and skirt portion and receiving sealingly relatively to the surroundings the cap attached on the container for ensuring the interior sterility of the container preceding the sterile filling of said container. The protective cap may be designed in such a way that it constitutes a cap sealing after the filling of the container.