Fixing system for a modular leading edge (2) to the structure of an aircraft lift plane (1), in which the leading edge (2) has a covering (4) formed from a first lamina (5) and a second lamina (6) between which there is an interior airtight chamber, and the fixing system comprises a main attachment element (3) whose cross-section has a central element (13), a first arm (14) which is fixed to the first lamina (5) of the covering (4) of the leading edge (2), and a second arm (15) which is fixed to the second lamina (6) of the covering (4), and the central element (13) is in turn fixed to a covering (10) of the torsion box (8) of the structure of the lift plane (1).