|Length||4.97 mi (8.00 km)|
|West end||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.
- There have been proposals to make the southwestern section from the M4 to Llanelli a trunk road, which would be operated by the Welsh Assembly Government, but these have been rejected. 
- The local council has a policy to reject any planning application that would prevent or adversely affect the implementation of a dual carriageway between the M4 and Trostre. 
Settlements served by the road include:
- Ordnance Survey. "1:50,000 Landranger Map". Retrieved 13 April 2012.
- Carmarthenshire County Council (12 December 2002). "REVIEW OF TRUNK ROADS IN WALES 2002". Retrieved 13 April 2002.
- "Carmarthenshire Council - Unitary Development Plan: Transportation". Carmarthenshire County Council. Archived from the original on 28 December 2013.