The man fell 20 metres down a steep slope after walking along a trail 50 to 100 metres above the falls, the largest waterfall in Europe, straddling the border of the cantons of Schaffhausen and Zurich.
The man was apparently admiring the view from a platform when he fell, police spokesman Patrick Caprez told the ATS news agency.
He was on the side of the falls in Neuhausen-am-Rheinfall.
Police are seeking information from witnesses.
In particular, they want to speak to a pair of joggers, a man and a woman, who tried to help the man who died on the spot from his injuries.
The couple left when an ambulance arrived, police said.
Police issued an “urgent” appeal for the joggers to contact them.
According to a description issued by police, the man is about 30 years old, about 190 centimetres tall, of slim build, wearing a grey and blue jogging suit.
He had a three-day beard.
The woman is around 30 years old, with dark blond hair.
She was wearing a yellow jacket with grey sweatpants, police said.
A Rega emergency rescue helicopter was used in the bid to rescue the man who fell, with firemen and police divers also called to the scene.
Schaffhausen police are seeking any witnesses to the incident to telephone 052 624 24 24.