Dysprosium (Dy) is a chemical element with atomic number 66. It is one of the 17 rare earth metals. It was named by its discoverer, French chemist Paul Émile Lecoq de Boisbaudran, after the Greek word dysprositos which means "hard to get", since it took him dozens of attempts to finally isolate the element.

There are seven stable and naturally occurring dysprosium isotopes, and the heaviest one (¹⁶⁴Dy) is the most abundant one.

Like a few of the other rare earth metals, dysprosium is sometimes used in magnets, and in nuclear reactor control rods.