| Friedrich Kettler | |
|---|---|
 | |
| Duke of Courland and Semigallia | |
| Reign | 17 May 1587– 17 August 1642 |
| Predecessor | Gotthard Kettler |
| Successor | Jacob Kettler |
| Born | 25 November 1569 Mitau, Duchy of Courland and Semigallia |
| Died | 17 August 1642 (aged 72) Mitau, Duchy of Courland and Semigallia |
| Burial | Ducal crypt in the Schloss Mitau |
| Spouse | Elisabeth Magdalena of Pomerania |
| House | Kettler |
| Father | Gotthard Kettler |
| Mother | Anna of Mecklenburg |
| Religion | Lutheran |
Friedrich Kettler (Latvian: Frīdrihs Ketlers; 25 November 1569 – 17 August 1642) was Duke of Courland and Semigallia from 1587 to 1642.
He was the son of Gotthard Kettler, the first Duke of Courland. Until 1617, he ruled only the eastern Zemgale (Semigallia) portion of the duchy, while his younger brother, Wilhelm Kettler, ruled the western Courland portion. Friedrich ruled the entire duchy from 1617 onward, after his brother emigrated due to conflicts with the nobility.