The invention relates to a discharge spout for flexible bags, of the type comprising a rigid plastic body forming a discharge passage and having a tube (3) intended to be inserted between two walls of a flexible bag and joined to such walls by means of sealing. The tube (3) has a smooth outer surface and two opposite flat flaps (4) extending externally in a mid-plane of said tube (3). The outer surface of the tube (3) forms, together with the surface (6) of the flat flaps (4), a sealing surface. The outer surface of the tube (3) has a middle area (5a), that is in the axial direction of the tube, in which the distance to the axis (7) of the tube is maximum, separating two side sections (5b, 5c) in which the distance to the axis (7) is decreasing toward the ends of the tube.