Pen yr Helgi Du

is a mountain peak in the eastern part of the Carneddau in Snowdonia, North Wales.

It lies on the south-eastern flanks of Carnedd Llewelyn, and is linked to Carnedd Llewelyn over the col of Bwlch Eryl Farchog, a knife-edge ridge over the cliffs of Craig Yr Ysfa. Cwm Eigiau lies to the east and the Ffynnon Llugwy reservoir to the south. To the east of Pen yr Helgi Du is Pen Llithrig y Wrach (the slippery peak of the witch).