The Zimbabwean man – whose name was not yet made public on Sunday afternoon – was trying to rescue a tourist at the time.
State media in Zimbabwe says he was working for Sunway Safaris and he drove up from South Africa to the Zambian side of the falls.
He had taken a party of tourists to Devil’s Pool, close to the main falls, police say one of the tourists slipped, in rescuing him the guide lost his balance and fell.
His body was not yet recovered on Sunday afternoon; with a 90 metre drop, authorities said there was little chance of finding him alive.
The police want to ban tourists from going to the viewing point, saying at least one person falls to their death there each year.