A device (1) for balancing rotors (3) by material removal is disclosed, which comprises a milling tool (18) provided with a first and a second cutting regions (18a, 18B) disposed transversely of each other, to remove material in the presence of feed movements for cutting, directed both radially of a rotor (3) and tangentially of the outer surface (4) of the rotor (3), and comprising support and relative-movement means (2) for positioning and moving the milling tool (18) and rotor (3) relative to each other, which means engages the rotor (3) in a manner adapted to cause rotation of said rotor about its rotation axis (5) even while the milling tool (18) is removing material from the rotor (3).