Please cancel the previous Abstract and insert the following new Abstract. The invention relates to an expandable intragastric balloon, for implantation into the stomach of a patient, to reduce the volume thereof for the treatment of obesity. Said balloon is provided with at least one first flexible pouch, capable of shifting from a folded position to an expanded position by introducing an inflation fluid into the first pouch, said expanded position giving a functional form to the balloon. Said balloon is characterized in that it comprises a ballasting means, for making said balloon substantially heavy to improve the positioning thereof in the stomach.