Gian Gastone de' Medici (1671 – July 9, 1737) was the last Medici Grand Duke of Tuscany, from 1723 to 1737, and the last of the Medici except for his sister Anna Maria Luisa de' Medici .

He was the son of Cosimo III de' Medici, Grand Duke of Tuscany and Marguerite Louise d'Orléans.

He came to power over a Florence in decline, and although he made a start on needed reforms, his inherent indolence and depravity soon overtook him. On his death, the Grand Duchy passed to Francis, Duke of Lorraine, whom the European powers had picked to replace Gian Gastone, without troubling to consult anyone in Florence. Florence became part of the Habsburg Empire.