Pentrebach (sometimes written Pentre-Bach) is a village in the County Borough of Merthyr Tydfil, Wales. It lies on the east side of the River Taff opposite Abercanaid, South of Merthyr and North of Troedyrhiw. To the east of the village lies the Mynydd Cilfach-yr-Encil which rises up to 445 m. Pentrebach can be translated as "Little Village"

Pentrebach is part of the Plymouth electoral ward which covers Pentrebach, Abercanaid and Troedyrhiw. The village was founded at the time that John Josiah Guest built the Plymouth Ironworks in 1763. The name Guest became part of the Guest, Keen and Nettelfold company (GKN). In 1818 Anthony Hill took over ownership of the business. His House was later used as an old peoples home and today has been converted into a Brewers Fayre Restaurant with a Travel Inn attached.

The original Trevethick Railway, built in 1804, ran through the village on it way from Pennydarren to Abercynon. A tunnel still exists, which can be visited on the Merthyr Road. Locomotives had to tip their chimneys while going though this tunnel due to the tunnel clearance.

Pentrebach has its own railway station. This opened in 1886 on the standard gauge Taff Vale Railway which runs from Cardiff to Merthyr alongside the River Taff. The original purpose of the railway was to carry iron ore to Cardiff Docks.

In 1862, on the south side of the Village, The South Duffryn Colliery was opened with two shafts which were 250 m deep. At the height of the production there were some 1300 men employed there. An opencast mine was also located on the mountainside above the village.

The Plymouth Ironworks closed in 1882 and the South Duffryn Colliery ceased production in 1940.

After the war new industries were attacted to the village. In 1945 the Kayser Bondor Factory opened making underwear followed in 1948 by the establishment of the Hoover factory manufacturing washing machines. The factory later went on the produce the Sinclair C5 battery powered three wheeler car. More recently Linde has set up a factory in the village on a site where the South Duffryn Colliery was located.

Pentrebach has two clubs: The Hills Plymouth Cricket Club and the Pentrebach Working men's club. It also has an infants school and an Integrated Children’s Centre.

The mountain above Pentrebach has become popular with Hang Glider Pilots in recent years.