Device for the hot granulation of thermoplastic polymers, optionally expandable, which comprises: a) a die (1) containing a series of small plates (6), equipped with a series of extrusion holes, and a plurality of feeding ducts (3) situated inside the die body (2) in correspondence with the perforated small plates (6), lined with a material having a high thermal conductivity (4); b) a cutting chamber comprising a set of spraying nozzles (17) which create a jet of drops of a thermostat-regulating liquid for cooling the cut granules; c) a cutting system comprising a cutting plate (13) supporting a set of knives (15) arranged so that the cutting profile of the knife is radial with respect to the die.