| Pen y Boncyn Trefeilw | |
| Elevation M: | 646 |
| Prominence M: | 57 |
| Listing: | Hewitt, Nuttall |
| Language: | Welsh |
| Location: | Gwynedd, Wales |
| Range: | Berwyn range |
| Grid Ref Uk: | SH 96255 28339 |
| Topo: | OS Landranger 125 |
Pen y Boncyn Trefeilw is a subsidiary summit of Cyrniau Nod in north east Wales. It forms a part of the Berwyn range called the Hirnantau. It has two tops: Stac Rhos and Pen y Cerrig Duon. Pen y Cerrig Duon is now listed as a deleted Nuttall due to re-surveying.
The views from the summit are extensive, if unremarkable due to the featureless, flat moorland surroundings. The summit is marked by a small cairn, is which located only a few metres from a track road that continues on to the pass between Cyrniau Nod and Y Groes Fagl.[1]