Over the past twelve months the Catholic Church held a special Holy Jubilee Year of Mercy, which encouraged churches worldwide to focus and reflect more deeply on God's mercy, and also canonised Mother Theresa of Calcutta in September.
The two events prompted more worshippers to visit the Vatican this year.
The four million figure includes the pontiff's General and Special Audiences, audiences related to the Holy Jubilee Year of Mercy, as well as other regular prayers and liturgical celebrations.
It doesn't include Pope Francis' ministry outside of the Vatican in other parts of Rome or Italy, or his trips abroad.
Last year, around 3.2 million visited the Vatican.
