Locking system (10) for a sliding door (2) with respect to a constraint structure comprising a latch (4), associable to the sliding door (2) or to the constraint structure, rotatable or rotatably translatable between a configuration of locking and a configuration of release of the door (2), a keyhole member (6), connectable to the other between the constraint structure or the sliding door (2), which delimits a holding edge (8) that, in the locking configuration, is engaged by the latch (4) to prevent movement of the, sliding door (2) with respect to said structure, the keyhole member (6) being manually operable to move the holding edge (8) and the latch (4) apart, when the latter is in the locking configuration.