The Sado River (Portuguese pronunciation: [ˈsaðu]) is a river in Southern Portugal, and is one of the major rivers in the country. It flows in a South/North direction through 175 km from its springs in the Caldeirão hills before entering the Atlantic Ocean in an estuary in the city of Setúbal.

In Setúbal, its estuary is famous for being the habitat for a large community of bottlenose dolphins; there are 31 members of the community, of which all have been named (2007).

In its course, it crosses the city of Alcácer do Sal.

It is dammed in several places chiefly for agricultural reasons, such as growing rice, maize (corn) and other vegetables.