Device for synchronizing the tilt of a chair back and seat, of the type comprising a frame of the chair back (5), a frame of the seat (2) and a support (1) integral with the base of the chair, as well as at least one first crank (3), integral with the afore said frame of the chair back (5), and hinged (6, 7) at the rear to the frame of the seat (2) and to the support (1), and at least one second crank (4), hinged (8, 9) at the front to the frame of the seat (2) and to the support (1). The afore said first crank (3) and the second crank (4), with the frame of the seat (2), determine a articulated quadrilateral, wherein such a first crank (3) and such a second crank (4) lie substantially on skew lines.