Otto (died 4 November 1004), called Otto of Worms, was duke of Carinthia from 978 to 985 and again from 1002 until his death.

The only son of Conrad the Red, Duke of Lotharingia, Otto was appointed duke of Carinthia and margrave of Verona when Henry I, Duke of Carinthia, had unsuccessfully rebelled against the king and was deposed. In 985 he lost his duchy, but could retain the title of duke as "duke of Worms". After the death of the margrave, Otto received the March of Verona back. In 1002, Otto was a candidate for king of the Holy Roman Empire; but he withdrew and received the Duchy of Carinthia from the newly elected king Henry II, the former duke, in return. He was succeeded as duke by his son, Conrad.

Otto married Judith of Bavaria (died 991). They had the following known children:
• Henry of Speyer
• Brun (died 999), ruled as Pope Gregory V
• Conrad I, Duke of Carinthia (died 1011)
• William, Bishop of Strasbourg (died 1047)