All popes wear a special ring, named the fisherman's ring after Peter's initial job as a fisherman.
The ring Francis will wear was "in the possession" ring worn by Pope Paul VI's private secretary, Archbishop Pasquale Macchi, the Vatican said.
Unlike Pope Benedict XVI's ring, which was made of gold, Francis' will be made of gold-plated silver.
A picture of the ring provided by the Vatican shows a small face with a relief image of a bearded St. Peter holding the symbolic keys to heaven.
Clarifying the ring's lineage, the Vatican said the ring "was in the possession of Archbishop Macchi, Pope Paul VI's personal secretary," then was owned by another priest before being proposed as a papal ring to Francis by Cardinal Giovanni Battista Re, a former prefect of the Vatican's Congregation for Bishops.