Fitting for trimming the horizontal stabilizer of an aircraft made of composite material is taught. The fitting has side walls (2a and 2b) of a torsion box as well as joining elements (3a, 3b) which join the fitting (30) to the frames of the tail fuselage (1) of the aircraft, said side (2a, 2b) being joined together by means of a central element (4) which comprises a first end part (4a) joined to the first side wall (2a) of the fitting (30). A second end part (4b) is joined to the second side wall (2b) of the fitting (30). A central part (4c) joins together said end parts (4a, 4b). The fitting (30) has end elements (5a, 5b) which are joined to said side walls (2a, 2b) on their outer face. Owing to its greater rigidity in response to side load and vertical load stresses which tend to close the side walls (2a, 2b), the fitting has greater integration and simplicity of load path, for optimum structural behavior in response to the aircraft stresses.
