A medical bag having a seal separating its inner space into a plurality of partitions for separate sealed storage of medical liquids and aiming for preventing erroneous operation that an infusion is practiced under a non-opened condition without worsening sterilizing performance during the production of the bag. A weak seal 18 is formed by welding the top and bottom film layers of medical bag 10 along the entire width of the medical bag, so that partitions 20 and 22 are formed at the upper and lower part of the weak seal 18. An outlet port 12 is mounted to the medical bag at a strong seal 14A. The outlet port 12 is extended in the lower chamber 22 to a location adjacent the weak seal 18, so that top end 12A is opened to the lower chamber 22 at a location above the liquid level L . The outlet port 12 is, at its bottom end, formed with a communication hole 26, while the shaded part (valve portion 28) at the inner face of the medical bag is welded to the opposite surface of the outlet port 12, thereby closing the communication hole 26. The welding strength of the valve portion 28 is slightly stronger than that of the weak seal 18.
