Unlike skydiving which involves leaping from an aircraft, base jumpers take off with a parachute from a fixed point, usually a cliff or a bridge.
The two incidents took place some 900 kilometres (550 miles) apart one in the Alps and the other in the Pyrenees.
On Wednesday morning, a 34-year-old Swiss man living in the Mont Saxonnex ski resort was killed after jumping from a spot popular with base-jumpers in Haute-Savoie.
Firefighters said the man's parachute failed to open. He struck the cliff before hitting the ground, and was killed instantly.
The second victim was a 46-year-old man from Paris who jumped from the north face of Pic du Midi d'Ossau in the Pyrenees around midday.
Rescuers said the cause of the accident was also likely a problem with the parachute opening.
The man fell 700 meters (750 yards) and was found dead on arrival, according to firefighters.
A base jump is defined as a leap off a fixed high point the name being an acronym for Building, Antenna, Span (such as bridges) and Earth (natural settings).
The pursuit carries high risks. A Norwegian study published in 2007 concluded that base jumping is between five and eight times more likely than skydiving to result in injury or death.