Pentre-bach (Welsh for "small village") is a hamlet (one of several in Wales with similar names) in Powys, Wales,[1] in the former county and current Shire Committee Area of Breconshire or Brecknockshire.

It is located on the Afon Cilieni, a small tributary of the River Usk, between Brecon and Llandovery.

The hamlet has a pub called the "Shoemakers Arms"[2] or Tafarn y Crydd, and a former chapel, originally Calvinistic Methodist, named "Beili-du",[3][4] Welsh for "black yard".

The nearest church is in Llandeilo'r-Fan, 2 km to the NW, and the nearest shop is in Sennybridge, 4 km to the south.

Construction started of a railway line up the Cilieni valley, but was abandoned in 1867.