Otto I, Margrave of Hachberg-Sausenberg (1302 – 1384) was a member of the House of Zähringen.

He was the son of Margrave Rudolf I of Hachberg-Sausenberg and his wife Agnes, the heiress of Otto of Rötteln.

After his brother Henry died in 1318, Otto took up government of Rötteln and Sausenberg.

[2] From 1364, Otto I ruled jointly with his nephew Rudolf III.

In 1366, Otto and Rudolf donated an altar to the church in Sitzenkirch.