Saint Tydfil (died c. 480), Standard Welsh Tudful, was a 5th century female saint associated with Merthyr Tydfil in Glamorgan, south Wales.

According to legend, she was one of the many daughters of King Brychan of Brycheiniog. She is said to have met her death at Merthyr, around 480, by the hands of pagans; probably Welsh, although they were later said to have been Saxons. Her feast day is 23 August.