Synchronization assembly and plant for laying cables such as electric conductors, optical fibers, ropes or suchlike. The machines of the assembly and plant are distinct and independent with respect to each other and each includes unwinding members having at least a pair of capstans to unwind the cables, and corresponding traction/collection members having at least a pair of capstans to wind the cables fed from the relative unwinding members. The synchronization assembly and plant includes automatic adjustment members that adjust the speed of rotation of the capstans of at least two unwinding members or two traction/collection members of the laying machines, so as to maintain the winding/unwinding speed of the cables stretched by each machine substantially equal.