The ducal line of Schleswig-Holstein-Sonderburg-Plön-Rethwisch descended from the line of Schleswig-Holstein-Sonderburg-Plön. It was founded by Joachim Ernest II (born 5 October 1637; died 5 October 1700) who as the third son of the Duke of Plön, Joachim Ernest, received the estate of Rethwisch in Storman as his inheritance. He was a general to the Spanish royal house in the Netherlands and became a Roman Catholic in 1673.
The line laid claim to the domain of Plön, this was rejected however by the King of Denmark. John Ernest Ferdinand (born 4 December 1684; died 21 May 1729) appealed to the Supreme Court and was vindicated. He died without leaving living descendants.
| Reign | Name | Remarks |
|---|---|---|
| 1671 -1700 | Joachim Ernest II | Founder of the line |
| 1700-1729 | John Ernest Ferdinand | Son |