Vatican spokesman Father Federico Lombardi said the exact dates and the program for the trip, which will last several days, were still not fixed.
Francis is expected to be in Istanbul on Nov 30, the feast of St. Andrew, at the invitation of Ecumenical Patriarch Bartholomew I, spiritual head of the world's Orthodox Christians.
The Vatican confirmed the trip after the pope accepted a separate invitation from the Turkish government.
Former pope Benedict XVI made a trip to Istanbul in 2006 and prayed with a Muslim cleric in the famed Blue Mosque.
Francis, the first non-European pope in 1,300 years, has made three trips abroad since his election in March, 2013.
He is due to visit Albania next week and on Nov 25 he will address the European Parliament in Strasbourg, France.