A guiding unit for slabs comprising at least two rolls (10, 10′) connected to each other and adapted to rotate along a same axis X; wherein each roll comprises a first tubular element (12) and a second tubular element (5), which is external and coaxial to axis X and to the first tubular element and removable from said first tubular element; wherein cooling channels (3, 30) are provided in each roll between said first tubular element and said second tubular element for the passage of a coolant liquid; wherein each roll comprises a respective hub at its two ends; and wherein each hub is provided with cavities communicating with the cooling channels of the respective roll so as to define a path for the coolant liquid from a first end to a second end of the guiding unit crossing said at least two rolls.