The husband of Princess Caroline of Monaco exceeded the French motorway speed limit by more than 80 kilometres per hour (50 mph), a court heard.
The prince was doing 211km/h
Prince Ernst August of Hanover, 49, clocked 211 km/h (131 mph) on the main Paris-Lyon motorway in central France in June. The legal limit is 130 km/h (81 mph).
He was fined 728 euros ($820) and had his licence suspended for a month.
Correspondents say France has one of the worst road safety records in Europe, but has recently cracked down on dangerous driving.
Prince Ernst is a flamboyant figure who has become a regular target of the German tabloid press.
In 1998, he was fined more than 40,000 euros for breaking the nose of a TV cameraman outside his Hanover home.
And three years later he was fined a much larger sum for several incidents against journalists, after he was photographed urinating - supposedly on the Turkish pavilion - at the Hanover Expo 2000 exhibition.
The prince denied the incident, which caused outrage among Germany's Turkish community and prompted a protest by Ankara's ambassador.
In 1999, Prince Ernst married Princess Caroline, the eldest daughter of Monaco ruler Prince Rainier.