Sigismund I may refer to:
- Sigismund of Burgundy (died 524), King of the Burgundians
- Sigismund, Holy Roman Emperor (1368–1437)
- Sigismund, Archduke of Austria (1427–1496)
- Sigismund of Bavaria (1439–1501), Duke of Bavaria
- Sigismund I the Old (1467–1548), King of Poland and Grand Duke of Lithuania