Portoscuso (Sardinian: Portescusi) is a comune (municipality) in the Province of Sulcis Iglesiente in the Italian region Sardinia, located about 75 kilometres (47 mi) west of Cagliari and about 14 kilometres (9 mi) northwest of Carbonia. The languages used here are Italian and Sardinian Campidanese.

Portoscuso borders the following municipalities: Carbonia, Gonnesa, and San Giovanni Suergiu.

Human presence in this territory dates back to Neolithic times. Bronze Age sites include the ruins of several Nuraghe (e.g. Baccu Ollasta) and the rock shelter of Punta Niedda, where the bones of 6 individuals and various objects of the Bonnanaro culture were recovered in the 1940s.

The area was then frequented by the Phoenicians, followed by the Punics and the Romans of whose passage some evidence remains, in particular regarding the funerary aspect, with the necropolises in the San Giorgio and Piccinu Mortu areas.

In the Middle Age this territory, as the rest of the Sulcis region, was part of the Giudicato of Cagliari until 1258, then it was part of the Della Gherardesca possessions and later, from 1324, part of the Kingdom of Sardinia, one of the kingdoms forming the Crown of Aragon.

The town originated in the 17th century from a hamlet inhabited by tuna and coral fishermen. Its name came from the Catalan Puerto Escos (hidden port). It became a comune in 1853, during the rule of the House of Savoy.

Notable sights include the Spanish Tower (16th century), the church of Madonna d'Itria (17th century) and the Arsenal, known as Su Pranu (17th century).

The town is extremely proud of its famous tuna fishery, and is restoring the original buildings.