The Pope has chided the mafia for committing acts of evil and chasing after earthly power and wealth.
He warned mobsters that they would go to hell unless they repented and changed their ways.
"Blood-stained money, blood-stained power, you can't bring it with you to your next life," he said.
The Pope made the comments during a service attended by relatives of people who had been killed by the mafia.
The service was organised by civic group, Libera, and held near Rome on Friday. Bereaved relatives were pictured extending their arms to the Pope for comfort during the meeting.
The Catholic Church has taken a hard line in recent years against mobsters who espouse Catholic beliefs while running crime rackets and committing brutal acts of inhumanity against rivals and opponents.
Around a thousand people attended the service and prayer vigil, during which the names of murder victims were read out.
The Pope continued his appeal to mobsters to leave their life of crime.
"This life that you live now won't give you pleasure. It won't give you joy or happiness," he said.
"There's still time to not end up in hell, which is what awaits you if you continue on this path."