South Wales Mountain Sheep, sometimes called Nelson or Glamorgan Welsh are a native hill sheep breed of South Wales (like the Badger Face Welsh Mountain Sheep, another Welsh Mountain Sheep on the Ark of Taste). The South Wales Mountain Sheep is largest breed of Welsh mountain sheep, with round horns (though the ewes are always hornless), large head and thick neck, with dense wool that ranges from white to tan in color.

Early in the twentieth century the mountain flocks of South Wales shared the same flock book as the mountain sheep of North Wales. They have since developed coarser, dense fleece and been recognised as a distinct breed of their own. It is found chiefly in the hill districts of Glamorgan, Gwent and South of the Brecon Beacons.

Commercial pressures on sheep farmers have resulted in many breeders of South Wales Mountain sheep using larger lowland breeds of ram on their ewes to produce cross-bred lambs. Such cross-bred tend to produce a heavier carcass which supermarket buyers prefer. Larger carcasses obviously produce a better return for the farmer but this results in an inferior taste to that produced from pure-bred South Wales Mountain Sheep. The lamb is at its best from August through to January and this is when it feeds on grass or other forage crops. South Wales Mountain sheep meat is sweet to the taste and milder than the lamb that is reared in the meadows and valleys.