"These structures of sin, mafia structures, are against the gospel and mistake idolatry for faith," the pope added.
In Italy, many members of organised crime see themselves as part of a religious, cult-like group, invoking the help of saints and using religious figurines or statues in initiation rites.
The southern town of Oppido Mamertina made headlines in 2014 when locals carrying a statue of the Madonna diverted the route of a procession to pause at the home of a mob boss and tilted the statue slightly as if to kneel in a sign of respect.
"Today, let us remember all the victims and renew our commitment against mafias," Francis said.
In recent years, the Calabria-based 'Ndrangheta has overtaken Sicily's Cosa Nostra as the most feared and lucrative Italian crime group, making most of its money from drug trafficking. It has spread throughout the world.