A plant for manufacturing single-dose capsules for preparing beverages, comprising a conveyor (2) for advancing impermeable shells (101) in succession along a production line, which plant comprises at least: forming means (3) for forming individual beaker-shaped filters (105) of filtering material and for releasing each of the beaker-shaped filters (105) inside an impermeable shell (101), means for adjusting the level of each beaker-shaped filter (105) inside the relative impermeable shell (101), and welding means (5) for welding the upper edge of each beaker-shaped filter (105) to the upper edge of the impermeable shell (101) in which the beaker-shaped filter (105) is inserted.