A medical bag formed of a flexible material includes a front bag part and a rear bag part joined together to form a bag body. A closable liquid inlet port is provided in an upper part of the bag body. The medical bag further includes a deformable elongated member provided in the vicinity of the liquid inlet port on at least one of the front and rear bag parts. The elongated member is deformable so as to retain the liquid inlet port in an open configuration when the elongated member is in a deformed state.