The present invention relates to a container bag (1) for containing semen for artificial insemination of animals, of the types which are formed by at least two sheets (2.1, 2.2) of sealed thermoplastic material, forming a tubular body (3) with an inner hollow (4) divided by means of a central constriction (5) into first and second contiguous enclosures (7.1, 7.2) communicated by means of a cannula (6) secured in said constriction (5), which bag comprises a closure plug (10) for closing said cannula (6) secured to the bottom (13) of the second enclosure (7.2) of the inner hollow (4), means for securing the cannula (6) to the central constriction (5), and means for securing the closure plug (10) to the bottom (13) of the second enclosure (7.2).