A sill (1, 1′) for a lift door is manufactured with a method that includes the steps of providing at least one support element (2) and an upper profile (4) that defines at least a boundary surface (6) of a first groove longitudinal (8) for slidingly receiving a lift door. The support element (2) and the upper profile (4) are joined, placing a first demarcation profile (10, 10′) alongside the upper profile (4), so that a boundary surface (12) of the first demarcation profile delimits part of the first longitudinal groove (8). A sliding transversal cross-section of the first longitudinal groove (8) is adjusted by approaching/distancing the boundary surfaces (6, 12) and, having obtained a desired sliding transversal cross-section, constraining the mutual position of the first demarcation profile (10, 10′) and of the upper profile (4).