Described is a unit for filling containing elements (2) of single-use capsules (3) for extraction or infusion beverages, comprising: a line (4) for transport of containing elements (2) designed to contain a dose (33) of product; a station (SR) for filling the containing elements (2) comprising: at least a first containing seat (S1) designed to receive a dose (33); a substation (ST1) for forming a dose (33) inside the first containing seat (S1); at least a second containing seat (S2) designed to receive the dose (33) from the first containing seat (S1); a substation (ST2) for transferring the dose (33) from the first containing seat (S1) to the second containing seat (S2); devices (7) for moving the first containing seat (S1) between the forming substation (ST1) and the transfer substation (ST2) and vice versa; a substation (ST3) for releasing the dose (33) from the second containing seat (S2) to a containing element (2); further devices (8) for moving the second containing seat (S2) between the transfer substation (ST2) and the release substation (ST3) and vice versa.