The 180kg (400lb) creature was discovered on La Arena beach in the northern Spanish region of Cantrabria.
It is a member of the Architeuthis dux species, which have the largest eyes in the animal kingdom, the Huffington Post said.
These can be as large as a human head.
The massive squid — which was discovered in very good condition — has now been moved to Cantabria's Maritime Museum in Santander.
Scientists have frozen the animal are now deciding whether it will be displayed.
The first footage of a giant squid in its natural habitat was captured in 2004 but the mysterious animals have long been present in popular mythology.