He walked alone and in silence around the concentration and extermination camp in what was Nazi-occupied Poland where 1.1 million people, mostly Jews, were killed.
Pope Francis also met elderly survivors of the camp, kissing them on the cheeks and speaking to them softly.
He is on his third day of a visit marking 1,050 years since Poland's adoption of Christianity.
Francis has become the third Pope to walk through the main gate of Auschwitz, under its infamous inscription "Arbeit Macht Frei" - work sets you free.
But unlike his German and Polish predecessors, he is not speaking about the horrors that occurred there, says the BBC's Adam Easton in Warsaw.
Francis passed under the gates alone, wearing white robes and skullcap. After meeting the survivors, he placed a candle at the Death Wall, where prisoners were executed by the Nazis, before continuing on his own.
The Pope stopped to pray at the prison cell of Maximilian Kolbe, a Polish Catholic friar who sacrificed his life to save that of another man. The Church made him a saint in 1982.
Pope Francis knelt for many minutes in the underground cell, illuminated only by the light from a tiny window, the Associated Press news agency reports.
The Argentine Pope is on a five-day trip to Poland.
During a World Youth Day rally in the southern city of Krakow on Thursday, he urged compassion for migrants.
He told hundreds of thousands of people that "a merciful heart opens up to welcome refugees and migrants" - a statement that puts him at odds with Poland's anti-immigrant right-wing government.

Gordon Coventry, 52, must spend a minimum of 20 years in jail for killing Mr Adie in Tweed Avenue, Kirkcaldy, on Saturday 28 May 2016.
Mr Adie was found unconscious in the street and he died later the same day in the Victoria Hospital.
Coventry was convicted at the High Court in Dunfermline on Monday.
Det Ch Insp Raymond Brown said: "The investigation into Darren's murder was complex and Gordon Coventry's efforts to evade justice caused the family unnecessary additional suffering.
"However, due to the diligence, skill and professionalism of the officers involved in the inquiry, coupled with the support and assistance from the local community, we were able to identify him as being responsible through protracted and detailed investigations.
"My thoughts today are with Darren's family and friends who had to endure the most tragic of circumstances.
"I would like to thank them for their support during the investigation and although nothing can ever undo the wicked actions of Coventry, I hope this verdict brings them some sense of comfort."
The Pope has offered a private prayer at the former Auschwitz death camp.
[NEXT_CONCEPT]
A man has been sentenced to life in prison for murdering father-of-two Darren Adie by repeatedly stabbing him on the body in Fife.