Mynydd Mallaen (Welsh: [ˈmənɨð ˈmaɬai̯n]) is an expansive plateau to the northwest of Cilycwm in northeast Carmarthenshire, Wales.

It takes the form of an undulating plateau with steep slopes dropping away to the Towy valley to the east and those of the Gwenffrwd, Nant Melyn and Afon Cothi to the north and west.

Its highest point of 1516 feet or 462m at OS grid reference SN 723455 is surmounted by two Bronze Age cairns known as Crugiau Merched (which translates from Welsh as ladies' barrows).

Gold mining occurs on the south-eastern flank of the plateau, and was pioneered in the Roman period as soon as the area had been conquered ca 75 AD.

The skylark is plentiful due to the extensive rough pasture present below the main peaks which allows ground nesting of the species.

The numerous sessile oak groves along the sheltered hillsides host the common bluebell in the spring, as well as offering sanctuary to wildlife.

Large parts of the plateau is peat bog and wet underfoot, so care is needed in walking the top in the absence of clear footpaths.