Portuguese police said the seizure was the largest in Europe in recent years and the biggest in Portugal for 15 years.
Police localized and intercepted a 79-foot yacht at sea, a statement said. They boarded it and found 183 bales of cocaine on board.
Police suspect the cocaine belonged to an international drug-trafficking gang that was bringing cocaine into Europe through the Iberian peninsula.
Three men were arrested and taken to Portugal.
The operation involved police from Portugal, Spain, the Drug Enforcement Agency in the United States, and the United Kingdom’s National Crime Agency.
Authorities said they would release further details of the operation later Monday.