The 52-year-old man was with his wife and four children when detained at the Bajakovo frontier post in eastern Croatia on Thursday night, police spokesman Josip Grcanac was quoted as saying.
The drug, with a street value of some $800,000, was hidden under a false floor in the vehicle, added the spokesman.
The family were heading from Kosovo, where the suspect originally comes from, to Sweden. The wife and four children were not detained.
Croatia, which is lobbying to be able to join the European Union, is considered a key transit point for drugs, black market cigarettes and illegal immigration to Western Europe.