In a clip that's quickly gone viral, a young girl snatches the pontiff's hat as he leans in to kiss her on the cheek.
Catholic tour guide Mountain Butorac posted the video to Twitter on Wednesday with the caption, "Took my Goddaughter to meet the pope. She stole his hat!"
In a later post to Facebook, Butorac then tagged the parents of 3-year-old Estella Westrick from the US state of Georgia.
Butorac told US broadcaster CNN that the comic incident with Pope Francis occurred on Estella's first full day in Rome. "It was hilarious, everyone was laughing including the pope," he said.
The pope then smilingly retrieved his cap, known as a zucchetto, which is worn by Catholic clerics and other Christian clergy members, before the girl was returned to her family members.
Butorac offers Catholic pilgrimages to Rome, Italy, and regularly brings his clients to events held by the leader of the Catholic Church.