The Valdes Peninsula (Spanish: Península Valdés or En Peninsula Valdes) is a peninsula into the Atlantic Ocean in the Biedma Department of north-east Chubut Province, Argentina. Around 3,625 km2 (896,000 acres; 1,400 sq mi) in size (not taking into account the isthmus of Carlos Ameghino which connects the peninsula to the mainland), it is an important nature reserve which was listed as a World Heritage Site by UNESCO in 1999.

Peninsula Valdes is located in the Argentinean Province of Chubut. The peninsula of approximately 360,000 hectares reaches more than 100 kilometres eastwards into the South Atlantic Ocean. Its roughly 400 kilometres of shoreline include a series of gulfs, including the extensive Golfo San Matias to the North and Golfo Nuevo to the South, both covering several thousand square kilometres. The dynamic coastal zone features rocky cliffs of up to 100 metres in height, shallow bays and shifting coastal lagoons with extensive mudflats, sandy and pebble beaches, active sand dunes, and small islands. The wetlands, some of them today also recognized as a Wetland of International Importance under the Ramsar Convention, are associated with the tidal areas of the Peninsula and provide significant nesting and resting sites for numerous migratory shorebirds. The diverse terrestrial, coastal and marine ecosystems of Peninsula Valdes contain natural habitats of extraordinary value from both a scientific and a conservation perspective.