Frederick Casimir Kettler (German: Friedrich Casimir Kettler; 6 July 1650 – 22 January 1698) is Duke of Courland and Semigallia from 1682 to 1698.

Frederick Casimir is the son of Jacob Kettler and Louise Charlotte of Brandenburg.

In his reign, the Duchy loses its geopolitical position and becomes a territorial subject of interest to Sweden, Prussia and Russia.