The bodies of Kienge Lukonde and Kioni Kyanukenbe were discovered Monday in a car on a road near the southern city of Lubumbashi.
Local officials say one man had been shot in the head, the other in the heart.
They say the luxury car they were driving was not stolen, suggesting the killing was politically motivated. The French news agency AFP quotes a spokesman for the opposition Union of Federalists and Independent Republicans party as accusing the Kinshasa government of ordering the killings to silence political parties. The victims were both candidates for governor of Katanga, which produces most of the country's copper and cobalt.