A squirrel-cage rotor for asynchronous motors is provided with a lamination stack made of a magnetic material and a plurality of bars, the intermediate portions of which engage respective slots of the lamination stack; the end portions of the bars protrude with respect to the lamination stack at both axial ends of the rotor and are fixed to two shorting rings; a plurality of spaces are defined, axially, by the lamination stack and the shorting rings, and tangentially by the end portions of the bars; part of such spaces is engaged by stiffening blocks arranged in contact with the end portions of the adjacent bars