"If someone is gay and he searches for the Lord and has good will, who am I to judge?" The New York Times said Francis asked in response to a reporter's question.
The pope's comments were made during an 80-minute press conference with reporters on his flight back to Rome, his first meeting with press since he was named pontiff in March.
He also defended gays from discrimination, RTE News reported.
"The Catechism of the Catholic Church explains this very well. It says they should not be marginalized because of this [orientation] but that they must be integrated into society," he said.
"The problem is not having this orientation," he added. "We must be brothers. The problem is lobbying by this orientation, or lobbies of greedy people, political lobbies, Masonic lobbies, so many lobbies. This is the worse problem."
Francis had spent the previous week in Brazil participating in activities marking World Youth Day. His final mass Sunday -- an open-air event on Copacabana Beach -- was estimated to have drawn as many as 3 million people, The Times reported.
"I profoundly thank all those who have worked to make WYD a success and I embrace all of you who were present," the pontiff said in a Twitter message on his return home, Italy's ANSA news service reported.
"I will always place my hopes in the young people of Brazil and in the young around the world," Francis told a crowd at Rio de Janeiro's as he prepared to fly back to Rome. "Through them, Christ is preparing a new springtime all over the earth."