The former warden of Reggio Calabria prison, Maria Carmela Longo, was arrested Tuesday night on suspicion of external conspiracy for mafia association.
Longo was placed under house arrest.
Prosecutors said they had found "systematic violation of the norms of penitentiary regulations and circulars from the penitentiary administration" in order to favour organised crime.
A preliminary investigations judge said Longo had "handed over Panzera Prison to mafia inmates".
Longo is currently director of the women's section of Rome's Rebibbia jail.