A packaging article using a thermoplastic film or sheet as a raw material therefor. The packaging article is provided with a bag opening in a region thereof. In forming the article, a front bag panel and a back bag panel are thermally fused together along their peripheral edges except the region defining the bag opening, into a bag form. The bag opening is associated with a flap for closing the same which is formed by extending either the front bag panel or the back bag panel and which has a reinforcing body thermally fused thereto. The reinforcing body is in the form of a laminate consisting of paper or synthetic paper having a thermoplastic layer applied thereto by lamination or by extrusion coating, which thermoplastic layer is thermally fused to the flap simultaneously with thermal fusion of the front and back bag panels. The reinforcing body is provided with an adhesive strip having a length extending throughout the width of the bag opening and a width such that when the flap provided with the reinforcing body is turned in, the adhesive strip is capable of joining the front and back bag panels to seal the entire bag opening. The reinforcing body assists in displaying the packaging article and it extends along the front or back bag panel to maintain or secure the configurational stability of the packaging article.