Ordulf (sometimes Otto) (c. 1022 – 28 March 1072) was the duke of Saxony from 1059, when he succeeded his father Bernard II, until his death. He was a member of the Billung family.
His entire reign was occupied by wars with the Wends. He was allied with Denmark, strengthening the alliance by marrying (1042) Wulfhild (died 24 May 1071), daughter of Olaf II of Norway. Their son Magnus succeeded Ordulf as Duke of Saxony.
His second wife, Gertrude of Haldensleben, daughter of a Count Conrad, was imprisoned in Mainz in 1076 and died 21 February 1116. Their son Bernard died after a fall from a horse at Lüneburg on 15 July (year unknown).
Ordulf is buried in the church of Saint Michael at Lüneburg.