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.

[1] 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: