The Telegraph reported that Sister Roxana Rodriguez was rushed to hospital after complaining of stomach pains.
She gave birth to the baby boy, who weighed nearly 9 lbs, at San Camillo de Lellis hospital 50 miles north of Rome.
Sister Roxana named the child Francesco in honour of Pope Francis.
The child’s father is reportedly believed to be in El Salvador.
Roxana said: ‘I will definitely take care of my baby because he is a gift of God… I called him Francis in honour of our South American pope.’
The 33-year-old nun thought that she was suffering from cystitis and an on-going stomach infection. She was also under the impression that her swollen belly was a result of poor digestion.
The birth of the child has caused outrage in the Catholic Church and Roxana faces expulsion from her convent in El Salvador.
Roxana took a vow of ‘poverty, chastity and obedience’ when she decided to become a Nun a few years ago and the vow means that Sister Roxana is forbidden from having sex.
Roxana revealed to a social worker that she was worried about the consequences of the baby’s arrival.
She said: ‘I am very worried about the commotion that this has stirred up. They are talking about this, not only in Italy but in my own country and I am afraid to return there.’
Roxana has written a letter of apology to her mother superior for breaking her vows.
The head of Roxana’s convent, Sister Erminia Pusceddu said: ‘she did not know how to resist temptation.’
The hospital where Roxana gave birth has been helping the new mother adjust to her new role and the local mayor has been offering her help with donations of nappies.