The invention relates to a de-entrainment device for a mass transfer tower. The de-entrainment device comprises a downwards-angled deflector which is positioned to be vertically aligned to the inferior of a hole mouth in a tray plate. The deflector is at least provided with a blade which is arranged to longitudinally extend and is in angulation relation with a horizontal plane and a vertical plane, and at least one vertically-arranged support foot which extends from the deflector and is used for installing the deflector under the tray plate.