The 69-year-old from New Zealand and a 58-year-old Irish nun became stuck on Friday at the Marist convent after an electrical power failure.
They cried out for help but there was no-one in the building over the weekend, Italian media said.
They were discovered on Monday by a cleaner who called police after ringing the doorbell and receiving no reply.
The police entered the building and called out if anyone was there and the nuns replied: “Yes, we are here, in the elevator”, according to Il Messaggero.
The two women later said they had “prayed so much” while trapped, Il Messaggero reported.
They were taken to a nearby hospital where they were treated for dehydration.
The Marist Sister House host visitors to Rome from religious missions around the world.