Abstract: A blood collector comprising a collection container in the form of a tube having a forward end adapted for drawing of blood into the container and an opened rear end, a closure unit adapted for closing the opened rear end of the collection container, and a mechanism including a valving element for allowing passage of air when blood is flowing into said container and preventing passage of air and blood when said container is filled with blood, said valving element of said mechanism including an air passage and a filter member communicating with the air passage, said filter member comprising water insoluble but water-swellable polymeric material and provided at least at the contact portion of the closure member with collected blood. Air contained in the blood collecting space of the collection container is expelled through the valving element by the collected blood which rises to a desired level for expelling air from said space practically completely.