Llanbrynmair or Llanbryn-mair (Welsh pronunciation^ⓘ) is a village, community and electoral ward in Powys, Wales. It is on the A470 road between Caersws and Machynlleth, and had a population of 920 in 2011.

The community includes several hamlets: Talerddig, Dolfach, Bont-Dolgadfan, Pandy, Cringoed, Dylife and Pennant. The original centre is at Llan, on the road to Llanidloes, where the local parish church of St Mary is located. The current centre (formerly called "Wynnstay") at the junction of the A470 and B4518 rose to local prominence with the building of the new turnpike road in 1821 and the arrival of the railway line between Newtown and Machynlleth in 1861.

Geographically, the community includes the valleys of three rivers – Afon Twymyn, Afon Iaen and Afon Rhiw Saeson – and the surrounding uplands. The three rivers join around the main village and flow westwards as the Afon Twymyn towards the Afon Dyfi and Cardigan Bay.

The Cambrian railway line, built in the 1860s, runs through Llanbrynmair and for a time provided an outlet for the mines at Dylife, 8 miles (13 km) south. The village station closed in 1965 as part of the "Beeching cuts". There was a level crossing next to the station but, following the accidental death of an American visitor in October 1999 and its description as a "blackspot", the crossing was closed and the road diverted. On 21 October 2024 two trains collided at Talerddig, near the site of the former station, resulting in one fatality and 15 injuries.

The area is predominantly Welsh-speaking and reliant upon livestock farming. It was fortunate to escape the foot and mouth disease outbreak in Britain in 2001.

In October 2024 the village became the first area in the UK where every resident had access to full fibre broadband.

The village was historically in Montgomeryshire.

Much of the area was part of the large Wynnstay Estate owned for generations by the families of Sir Watcyn Williams Wynne. The connection is noted in the "Wynnstay Arms", a prominent local public house.