System for butt-joining two or more rubber strips (B1, B2) selected in accordance with a predetermined rubber mixture recipe in order to feed at least one extruder with a complex strip of rubber material (B 12) made from the butt-joined rubber strips, wherein the system comprises: at least one conveyor that transports the rubber strips from an inlet of the system to an outlet of the butt-joining system; a frame that operationally supports the conveyor to allow the continuous transport of the rubber strips and also to allow the simultaneous butt-joining of the rubber strips fed to the system; and a roller system that butt-joins the rubber strips without penetration, the roller system comprising at least one upper roller and one lower roller (24, 24'), each roller having a center through which an axis of rotation of the roller extends and each roller having a cylindrical body of predetermined diameter that extends perpendicularly and rotates about its axis of rotation with respect to the frame that supports the roller system, the two rollers (22, 24) being disposed such that the two axes of rotation remain in the same plane with the axes parallel to one another, and the upper roller having a toothed surface along which a length of contact is established between a first fed rubber strip (B 1) and the toothed surface while the first rubber strip (B 1) passes through the roller system, the toothed surface comprising a plurality of teeth disposed consecutively along a common axis defined with respect to two opposite ends (22a', 22a") of the cylindrical body of the upper roller, and the lower roller comprising a smooth surface along which a length of contact is established between a second fed rubber strip and the smooth surface while the second rubber strip passes through the roller system, the smooth surface 24b comprising a circumferential surface that has a bearing surface between two opposite ends (24a', 24a") of the cylindrical body of the lower roller. at least one conveyor that transports the rubber strips from an inlet of the system to an outlet of the butt-joining system; a frame that operationally supports the conveyor to allow the continuous transport of the rubber strips and also to allow the simultaneous butt-joining of the rubber strips fed to the system; and a roller system that butt-joins the rubber strips without penetration, the roller system comprising at least one upper roller and one lower roller (24, 24'), each roller having a center through which an axis of rotation of the roller extends and each roller having a cylindrical body of predetermined diameter that extends perpendicularly and rotates about its axis of rotation with respect to the frame that supports the roller system, the two rollers (22, 24) being disposed such that the two axes of rotation remain in the same plane with the axes parallel to one another, and the upper roller having a toothed surface along which a length of contact is established between a first fed rubber strip (B 1) and the toothed surface while the first rubber strip (B 1) passes through the roller system, the toothed surface comprising a plurality of teeth disposed consecutively along a common axis defined with respect to two opposite ends (22a', 22a") of the cylindrical body of the upper roller, and the lower roller comprising a smooth surface along which a length of contact is established between a second fed rubber strip and the smooth surface while the second rubber strip passes through the roller system, the smooth surface 24b comprising a circumferential surface that has a bearing surface between two opposite ends (24a', 24a") of the cylindrical body of the lower roller.