The former Merthyr Synagogue is located on Bryntirion Road in the Thomastown section of Merthyr Tydfil, Wales. It is a Grade II listed building and is the oldest purpose-built synagogue still standing in Wales.
The Jewish congregation of Merthyr was established in 1848 at a time when Merthyr Tydfil was a centre of the industrial revolution and the largest town in Wales. The new congregation called itself the "Merthyr Tydfil Hebrew Congregation", and erected its first synagogue in 1852–1855 in John Street. That first building was demolished in the 1990s.
The 1855 building was replaced by the prosperous congregation with the surviving synagogue building in 1877. The congregation had 27 head-of-household members in 1900. The 2011 census recorded four.
The congregation, which had been dwindling, rededicated the synagogue in 1955. In the 1980s, the synagogue was closed and the building was sold and became the Merthyr Chri