|Length||4.97 mi (8.00 km)|
|East end||A48 at Pontarddulais|
|West end||A484 at Parc Trostre|
The A4138 is a main road in Carmarthenshire, Wales, connecting Pontarddulais with Llanelli. Running in a northeast to southwest direction, the road connects with M4 junction 48. Northeast of the motorway, the road is classified as a non-primary route, while southwest of the motorway, the road is classified as a primary route. In both instances, the road is operated by Carmarthenshire County Council.
Settlements served by the road include: