A Brazilian man carrying the two cushion-like implants, which were attached to a pair of swimming trunks, was detained by Portugal's anti-narcotics agency.
Later, another man was arrested at a train station under suspicion of being due to receive the drugs.
It is not yet clear how police discovered the haul.
The cocaine stashed in the fake buttocks was equivalent to at least 5,000 individual portions of the drug, police said.
Drug possession and use is decriminalised in Portugal, but drug trafficking may incur prison sentences of up to 12 years.