Described is an ultrasonic device for sealing material (1) in strips, comprising: a generator (9) of electrical power signals; a converter (9a) for converting the electrical power signals into mechanical vibrations; a sonotrode (2) rotating about a first axis (X2); an anvil (4) rotating about a second axis (X4) parallel to the first axis (X2); the sonotrode (2) having a circular groove (6) and the anvil (4) having a protruding element (7) which is annular in shape; the protruding element (7) is configured to operate in conjunction with the groove (6) along directions parallel to the first axis (X2) and to the second axis (X4) in such a way as to seal the sheet or strip of material (1) moved along a direction (A) transversal to the first (X2) and second (X4) axis of rotation and passing between the sonotrode (2) and the anvil (4) engaging the groove (6) and the protruding element (7).