| Friedrich Wilhelm II | |
| Succession: | Duke of Saxe-Altenburg |
| Reign: | 1639–1669 |
| Predecessor: | Johann Philipp |
| Successor: | Friedrich Wilhelm III |
| Spouse: | Sophie Elisabeth of Brandenburg Magdalene Sibylle of Saxony |
| Issue: | Christian, Hereditary Prince of Saxe-Altenburg Johanna Magdalena, Duchess of Saxe-Weissenfels Friedrich Wilhelm III, Duke of Saxe-Altenburg |
| House: | House of Wettin |
| Father: | Friedrich Wilhelm I, Duke of Saxe-Weimar |
| Mother: | Anna Maria of the Palatinate-Neuburg |
| Birth Date: | 12 February 1603 |
| Birth Place: | Weimar |
| Death Place: | Altenburg |
Friedrich Wilhelm II (12 February 1603, in Weimar – 22 April 1669, in Altenburg), was a duke of Saxe-Altenburg.
He was the youngest son of Friedrich Wilhelm I, Duke of Saxe-Weimar, and Anna Maria of the Palatinate-Neuburg, his second wife. He was born eight months after the death of his father, on 7 July 1602.
Shortly after his birth, Friedrich Wilhelm II and his older brothers inherited Saxe-Altenburg as co-rulers under the guardianship of the Electors of Saxony Christian II and John George I until 1618, when his older brother John Philip assumed the government of the duchy and the guardianship of his younger siblings.
By 1632, two of his three brothers were deceased. Friedrich Wilhelm II and his older brother John Philip began a joint government; but, in fact, John Philip was the real and only ruler of the duchy of Saxe-Altenburg. Friedrich Wilhelm II was only a nominal ruler until the death of John Philip (1639), when he began his personal reign over Altenburg.
At Altenburg Castle on 18 September 1638 Friedrich Wilhelm II married his first wife, Sophie Elisabeth, the only daughter of Christian William of Brandenburg. She died in 1650 after twelve years of childless marriage.
In Dresden on 11 October 1652 Friedrich Wilhelm II married secondly Magdalene Sibylle of Saxony, Dowager Crown Princess of Denmark and daughter of his former regent, the Elector John George I. They had three children:
In 1660 he acquired the towns of Themar and Meiningen. In 1664 he built a hunting seat (German: [[Jagdschloss]]) in Hummelshain, and, in 1665, he built a particularly beautiful widow seat (German: Witwensitz) called "Magdalenenstift" in Altenburg for his wife Magdalene Sybille.
After his death he was succeeded by his second and only surviving son, Frederick William III.
