| Country: | Wales |
| Official Name: | Llwyncelyn |
| Coordinates: | 51.6132°N -3.3986°W |
| Unitary Wales: | Rhondda Cynon Taf |
| Lieutenancy Wales: | Mid Glamorgan |
| Constituency Westminster: | Rhondda |
| Constituency Welsh Assembly: | Rhondda |
| Post Town: | PORTH |
| Postcode District: | CF39 |
| Postcode Area: | CF |
| Dial Code: | 01443 |
| Os Grid Reference: | ST032914 |
Llwyncelyn is a district of Porth, Rhondda Cynon Taf.
Consisting of five long terraces and two modern housing developments, Llwyncelyn has one shop and a parish church, St. Luke's Church.
Llwyncelyn is also where Porth Harlequins RFC play their home rugby union matches.
Nearby Nyth-Brân Farm was the home of athlete Guto Nyth Brân.