Their car swerved off the track after a notoriously difficult crest during a race not connected to the main rally championship, according to officials.
German rally organisers said they had cancelled the final stage of the day in response.
"Two Dutch participants died in an accident on Saturday for yet unknown reasons at the historic demonstration race 'Classic'. Despite immediate rescue efforts the two men died on the spot," Trier police said in a statement.
The accident took place at the Arena Panzerplatte, a former tank training facility, with the car leaving the track after the "Gina" jump, which catapults cars some 40 metres.
"The car, driven by a Dutch pairing, left the route near the Gina crest," said organisers of the German rally.
"The emergency services were on the scene immediately to assist but despite their best efforts the injuries sustained by both the driver and passenger proved fatal. No one else was involved in the incident."
The identities of the driver and co-driver were not released.
The accident happened after the World Rally Championship cars had passed. Organisers cancelled special stage 14 but decided to continue the rally on Sunday as scheduled.
"The second passage of Arena Panzerplatte has been cancelled and the competition cars have been re-routed back to the Service Park in Trier," they said. "The rally will continue on Sunday according to its itinerary."
(Reporting by Karolos Grohmann, editing by Stephen Wood)
