The unnamed sisters, a 69-year-old from New Zealand and a 58-year-old from Ireland, entered the lift at the Marist Sister House in Rome before the power went down just before the building's closure.
The convent welcomes members of religious missions from across the globe. The pair were only in the city to visit.
It wasn't until a cleaner arrived on Monday unable to get in that their cries for help were heard.
According to Italian newspaper Il Messaggero, the nuns said they had "prayed so much" for someone to find them.
Police soon rescued them and they were taken to a nearby hospital, where they were treated for dehydration.
