The incident occurred around 7.30am when for reasons not immediately known the ULM ploughed into the east face of the 2,002-metre-high mountain, ten metres from the peak, Fribourg cantonal police said.
The aircraft subsequently plunged 100 metres down the mountainside, police said.
Emergency rescue workers from the nearby town of Bullle and a helicopter crew from Rega responded to the accident but the pilot, a resident of the canton of Vaud, was already dead.
Le Moléson, a local landmark, overlooks the village of Gruyères in the Gruyère cheese-making region and is a popular tourist destination, served by a funicular railway and cable car.
To allow police and other emergency officials to respond to the crash, the cable car taking visitors to the summit was closed for several hours, police said.
The victim had started his flight in Arc-sous-Cicon in the Doubs department of France, north of the Swiss border.
ULM aircraft have only been authorized to fly in Switzerland since last Wednesday when new regulations were introduced.
An investigation is under way to establish the cause of the crash.