Fixing system of a series of oblong elements (1, 2, 3, 4, 5, 6) for a structure for pieces of furniture, the fixing system comprising at least one joint element (7, 7', 7") which constitutes a coupling interface between at least two of the oblong elements (1, 2, 3, 4, 5, 6) in such a way that the reciprocal coupling of the series of oblong elements (1, 2, 3, 4, 5, 6) by means of a series of joint elements (7, 7', 7") and fixing means is suitable for the assembly of said structure, the joint element (7, 7', 7") comprising at least two arms (11, 12) a first arm and a second arm of which are reciprocally connected in correspondence with a connection zone, in which first arm and second arm are reciprocally inclined according to a first angle, the oblong elements (1, 2, 3, 4, 5, 6) being provided with a body having an elongated shape wherein the fixing system includes: - a hollow obtained in the body in correspondence at least with a first end of a first oblong element of the series of oblong elements (1, 2, 3, 4, 5, 6); - a first seat and a second seat of insertion obtained in correspondence with the first end of the first oblong element in such a way that each one of first seat and second seat puts into communication the inside of the hollow with the outside of the hollow; first seat and second seat of insertion being placed reciprocally spaced along the perimeter of the hollow according to a reciprocal positioning corresponding to the inclination according to said first angle, in such a way that the joint element (7, 7', 7") is insertable within the hollow according to a configuration in which the connection zone between the arms (1, 2) is housed inside the hollow, the first arm protrudes externally with respect to the hollow through the first seat constituting a first support element for a second oblong element, the second arm protrudes externally with respect to the hollow through the second seat, constituting a second support element for a third oblong element, said at least two arms (11, 12) being flat and the corresponding first seat and second seat of insertion of the arms have a long and narrow groove shape for insertion of a corresponding arm, the expression long and narrow referred to the groove meaning a groove shape in which a first side of the groove has dimension in length greater than the dimension in length of the second side of the groove, the width corresponding to the width of the flat shape of the arms, wherein at least one of the at least two arms (11, 12) has a shape comprising a bending and a counter-bending defining portions of the first arm comprising a first portion and a second portion which are reciprocally parallel and connected and spaced by a third portion included between the bending and the counter-bending, first portion and a second portion constituting engagement portions with internal walls of the internal hollow of one of said oblong elements. - a hollow obtained in the body in correspondence at least with a first end of a first oblong element of the series of oblong elements (1, 2, 3, 4, 5, 6); - a first seat and a second seat of insertion obtained in correspondence with the first end of the first oblong element in such a way that each one of first seat and second seat puts into communication the inside of the hollow with the outside of the hollow;