The Castro of Monte Valinhas, alternately the Castro of São João de Valinhas, is an archaeological site in Portugal, in the civil parish of Santa Eulália, in the municipality of Arouca, notable for the discovery of important traces of human remains from the last 2000 years.

Its situation, overlooking the open-spaces in the valley, was used by successive communities throughout the centuries (since the Neolithic until the Middle Ages) for protection and defence.

It was in this period that a defensive structure (castro) was established over Monte Valinhas, as well as along the southern and southeastern flanks, taking advantage of the granite rocks that exist there.

Later, during the Roman period, the area was reoccupied, possibly after the 1st century: artifacts that include fragments of ceramics and glass, lithics and metals were discovered during archaeological investigations.

Archaeological study of the area began in at the end of the 1980s, by a team of investigators coordinated by António Manuel Silva, whom identified the walled compound.