The US was offering a large reward for information on the brothers
Colombian police say they have killed one of the country's most notorious criminals and drug lords.
Media reports say the dead man is Victor Manuel Mejia Munera, although officials earlier said it was his brother, Miguel Angel.
Defence Minister Juan Manuel Santos said the man was killed in a shoot-out in the northern province of Antioquia.
The US had offered a reward of $5m (£2.5m) for information leading to the capture of the brothers.
Two bodyguards were killed during the shoot-out.
Colombian media reports say officials thought the dead man was Miguel Angel because of documents found at the scene, but that an autopsy suggested he was Victor Manuel.
In the criminal underworld, the Mejia brothers command fear and respect, says the BBC's Jeremy McDermott in Bogota.
They came to public notice in 2001 when $35m in cash was found in two apartments in Bogota.
The brothers were not only prominent drugs traffickers, but also led part of the new generation of paramilitary groups that sprang up after the demobilisation of the illegal United Self Defence Forces of Colombia, the AUC.