The corpse was found wrapped in bin liners inside a chest freezer at the elegant flat in the town of Borgomanero in the northwest Piedmont region.
The grim discovery followed a search of the apartment after the old woman's 60-year-old daughter, who lives there, called emergency services claiming she felt unwell. She was admitted to hospital under police guard.
Investigators believe woman's mother, who was born in 1932, may have been dead for four years or more.
They were trying to establish the cause of death and suspect her daughter may have continued to collect the old woman's pension, according to Turin-based daily La Stampa.