An automatic drop-down seal for doors is fitted to shut the gap between the door bottom and floor. It consists of an internal aluminum profile mounted within the door and of a second inner aluminum profile that is pushed downwards by a lever. The system is activated by a plunger that pushes against the door frame or on a specific external element when the door closes. Beginning from the plunger side, the internal profile drops downwards to complete its movement on the opposite side for a complete drop. This profile is equipped with a seal the type changes depending on the different models that stick to the floor closing the gap for all the length of the door.