Curt Knox and Edda Mellas were indicted in Perugia for libel, said the Italian news agency ANSA. Lawyer Luciano Ghirga confirmed the indictment and said trial was set for July 4.
He said the couple did not attend the hearing.
The charge stems from an interview they gave Britain's Sunday Times years ago in which the father alleged that police had physically and verbally abused his daughter during questioning after Meredith Kercher's 2007 slaying, before Knox was arrested.
Police have denied harming Knox.
A Knox family representative said there would be no comment.
Knox and ex-boyfriend Raffaele Sollecito were convicted in 2009 of sexually assaulting and murdering Kercher in the apartment she shared with Knox in the central Italian city of Perugia. Kercher was stabbed to death the night of Nov. 1, 2007.
Knox was sentenced to 26 years in prison; Sollecito 25 years. Both deny wrongdoing and their appeals trial is under way.
Another man, Rudy Guede, was also convicted in the killing. Italy's highest criminal court has already upheld Guede's conviction and his 16-year-prison sentence.