Vatican officials say a cap is needed to protect Michelangelo's delicate frescoes, which are being damaged by the increasing crowds.
Up to 20,000 people a day can visit the chapel where popes are elected.
But now the number will be limited to stop the deterioration of the 500-year-old paintings which include the arm of God giving life to Adam.
Body sweat, carbon dioxide and dust on shoes is said to be a major risk to the frescoes that the Vatican has already taken steps to protect.
Earlier this month it was announced that new LED lights would be installed inside the Sistine Chapel and a new air-regulating system is already in place.
Head of the Vatican Museums, Antonio Paolucci, said: "I am convinced that the Vatican Museums, in particular the Sistine Chapel, have reached the maximum number of visitors possible."
Currently around six million a year visit the chapel and that number will not be allowed to increase.
It is thought the current system of queuing outside will continue, but a reservation-only system has not been ruled out.