| Gwladus Ddu | |
| Birth Name: | Gwladus ferch Llywelyn |
| Death Place: | Windsor, Berkshire, Kingdom of England |
| Parents: | Llywelyn the Great and Joan Plantagenet |
| Relatives: | John, King of England (grandfather) Maud de Braose (daughter-in-law) |
| Spouse: | Reginald de Braose (c. 1215-1228) Ralph de Mortimer (c. 1230-1246) |
| Children: | 3, including Roger |
Gwladus Ddu, ("Gwladus the Dark Eyes"), full name Gwladus ferch Llywelyn (died 1251) was a Welsh noblewoman who was a daughter of Llywelyn the Great of Gwynedd and Joan Plantagenet, a daughter of John, King of England. She married two Marcher lords.
Sources differ as to whether Gwladus was Llywelyn's legitimate daughter by his wife Joan or an illegitimate daughter by Tangwystl Goch, but she is widely regarded to be the daughter of Joan. Gwladus is recorded in Brut y Tywysogion as having died at Windsor in 1251.