Ferdinand III can refer:

• Ferdinand III of Castile, the Saint (1199-1252, king from 1217)
• Ferdinand III of Naples (1452-1516, king from 1504) (= Ferdinand V of Castile 1474-1504) (= Ferdinand II of Aragon from 1479 and of Sicily from 1468)
• Ferdinand III, Holy Roman Emperor (1608-1657, emperor from 1637)
• Ferdinand III of Sicily (1751-1825, king 1759-1816) (=Ferdinand IV of Naples 1759-1799; 1799-1806; 1815-1816)
• Ferdinand III of Tuscany (1769-1824, grand-duke 1791-1799 and 1814-1824)