Abstract: A structural joint device for foldable chairs includes a combination of three tubular elements one of which has the shape of a rectangular frame forming the front legs and backboard of the chair. Another of the tubular elements has the form of a U-shaped tubular profile forming the back legs of the chair, while the third tubular element has the shape of a rectangular or quadrangular frame forming the seat frame of the chair. Lateral members of the three tubular elements are connected to one another by a pair of lateral structural joint devices. Each of the structural joint devices comprises a pair of identical rectangular prismatic pieces, one of which is partially inlaid and fixed to the corresponding interior face of the lateral member of the tubular element forming the front legs and backboard, while the other piece is placed facing the latter and is fixed on the lateral member of the tubular element forming the seat frame.