Estella Westrick was taken to meet the head of the Catholic church at his weekly papal audience in Rome today.
The young girl was lifted up by her godfather Mountain Butorac after being called forward by a security guard.
But as the 80-year-old Pontiff kissed her on the cheek, she reached up and took his cap, known as a zucchetto.
Pope Francis burst into laughter, and the young girl was spotted on video smiling afterwards, as the Pope reclaimed his skullcap and put it back on.
She had been visiting her godfather, a Rome resident, on holiday from Atlanta, Georgia.
Pope Francis burst into laughter when three year old Estella Westrick stole his zucchetto
It was hilarious. Everyone was laughing, including the Pope
Mr Butorac, Estella's godfather
Mr Butorac said: “Right before she went up she was a little nervous.
“Then she stole his hat. It was hilarious. Everyone was laughing, including the Pope.
“It was her first full day in Rome, who knows what she will get up to tomorrow.”
Pope Francis attended his weekly audience in St. Peters Square in Rome
Get Quotes on Home Insurance
The youngster’s parents, who were present at the time, were “horrified” initially but later found the incident funny.
Mr Butorac said the family had arrived hours ahead of the appearance at 7am to secure a good spot in the audience.
He tweeted: “Took my Goddaughter to meet the pope. She stole his hat.”
Pope Francis had his zucchetto taken by a child previously in 2013 Pope Francis in pictures Sun, February 5, 2017
The very best photographs of Pope Francis.
Play slideshow REUTERS 1 of 97
Pope Francis receives a parrot from a performer of the Golden Circus during his Wednesday general audience in Paul VI Hall at the Vatican
It is not the first time a curious child has taken Pope Francis’ headwear.
In 2013, a child took his white zucchetto while being held by the Pope at the Vatican.