The bulk of the high-purity heroin, 263 kilos, was found hidden in a shipment of cement that arrived at the port of Barcelona from Turkey, Interior Minister Juan Ignacio Zoido told a news conference.
The rest was found in the homes of four suspects arrested as part of the operation and during a botched transaction they tried to carry out, he added.
The four -- a Spaniard, an Ecuadorian and two Dominicans between the ages of 30 and 45 -- have been charged with drug trafficking, membership in a criminal organisation and illegal possession of weapons.
The amount of heroin that was seized in this operation surpasses the 253 kilos of the drug that was apprehended during all of last year by Spain's various police forces, the ministry added.