Aeddan ap Blegywryd (died 1018) was a Prince of Gwynedd in medieval Wales. After the death of Cynan ap Hywel in 1005, the throne of Gwynedd fell to Aeddan ap Blegywryd, who was apparently out of the direct line of succession. It is not known whether or not Aeddan seized the throne by force, but his lack of connection to the ruling family of Gwynedd suggests that he did. He reigned until 1018, when he was defeated in battle by Llywelyn ap Seisyll and killed together with his four sons.