Unit for stacking slats on a support ladder for the production of Venetian blinds, the ladder comprising two parallel uprights (P1, P2) connected transversally by a plurality of pairs of crossbeams (T1, T2), said unit comprising: - at least one guide element for a slat, defining an insertion plane (m) on which the slat slides supported along a longitudinal insertion axis, at said plane (m) the slat being inserted between two crossbeams of a ladder positioned on a positioning plane (p) incident to the insertion plane (m), with the two uprights positioned on two opposite sides of the longitudinal axis; and - means for divaricating at least one pair of crossbeams (T1, T2) on the positioning plane (p) at the height of the insertion plane (m), in such a way that one crossbeam is placed below said plane (m) and the other crossbeam is placed above, so as to permit the insertion of the slat between the two crossbeams, whereby the divaricating means comprise - two distinct divaricating elements (11, 12), each of which is sized so as to be inserted between a pair of crossbeams (T1; T2) substantially without divaricating them; characterised in that it comprises - an actuating device which supports both divaricating elements (11, 12) and is suitable to make them alternatively adopt a first operating configuration, in which the two divaricating elements (11, 12) are arranged close to each other or alongside, and at least a second operating configuration, in which the two divaricating elements (11, 12) are distanced from each other, the actuating device being movable in relation to the insertion plane (m) and to the positioning plane (p) so as to move the two divaricating elements (11, 12) together into an engagement position, in which both divaricating elements are incident to the positioning plane (p), and at least one disengagement position, in which the divaricating elements are not incident to the positioning plane (p). - at least one guide element for a slat, defining an insertion plane (m) on which the slat slides supported along a longitudinal insertion axis, at said plane (m) the slat being inserted between two crossbeams of a ladder positioned on a positioning plane (p) incident to the insertion plane (m), with the two uprights positioned on two opposite sides of the longitudinal axis; and - means for divaricating at least one pair of crossbeams (T1, T2) on the positioning plane (p) at the height of the insertion plane (m), in such a way that one crossbeam is placed below said plane (m) and the other crossbeam is placed above, so as to permit the insertion of the slat between the two crossbeams, whereby the divaricating means comprise - two distinct divaricating elements (11, 12), each of which is sized so as to be inserted between a pair of crossbeams (T1; T2) substantially without divaricating them; characterised in that it comprises - an actuating device which supports both divaricating elements (11, 12) and is suitable to make them alternatively adopt a first operating configuration, in which the two divaricating elements (11, 12) are arranged close to each other or alongside, and at least a second operating configuration, in which the two divaricating elements (11, 12) are distanced from each other, the actuating device being movable in relation to the insertion plane (m) and to the positioning plane (p) so as to move the two divaricating elements (11, 12) together into an engagement position, in which both divaricating elements are incident to the positioning plane (p), and at least one disengagement position, in which the divaricating elements are not incident to the positioning plane (p).