Gweunydd Glan-y-glasnant is a Site of Special Scientific Interest (SSSI) in Carmarthenshire, Wales, designated in 1993 for its botanical features.

[1][2] Gweunydd Glan-y-glasnant SSSI is a set of unimproved cattle-grazed pasture and hay meadows, extending to 12.5 hectares (31 acres), on varying thicknesses of glacial till overlaying coal measures and shaley sandstone.

[1][2] The site is designated as an SSSI for its species-rich neutral grassland, rare now in Great Britain with 97% of such land lost through agricultural improvements since 1930.

There are smaller communities of tormentil (Potentilla erecta), meadow vetchling (Lathyrus pratensis), yarrow (Achillea millefolium), self-heal (Prunella vulgaris), as well as common spotted-orchid (Dactylorhiza fuchsii) and the adder's-tongue fern (Ophioglossum vulgatum).

A distinct part of the site is a fen-meadow hosting purple moor-grass (Molinia caerulea) and meadow thistle (Cirsium dissectum).