Brycheiniog was a small independent petty kingdom in South Wales in the Early Middle Ages. It can also refer to:
- Places
- Fan Brycheiniog, highest peak in the Black Mountain region of the Brecon Beacons National Park in South Wales
- Theatr Brycheiniog theatre in Brecon
- Bannau Brycheiniog, Welsh name for Brecon Beacons, Wales
- Bannau Brycheiniog National Park, alternative name for Brecon Beacons National Park, Wales
- Welsh name for Borough of Brecknock, Wales
- People
- Gwynfardd Brycheiniog (fl. c. 1170-80), Welsh poet
- Brychan (or Brychan Brycheiniog), legendary 5th-century king of Brycheiniog
- Other
- Brycheiniog (magazine), journal founded in 1955 and published by the Brecknock Society and Museum Friends