The movie star, who won an Oscar for her role in the 1995 anti-death penalty film "Dead man Walking" actress, said she had sent a copy of the book on which the movie is based to the pope.
"The last one. Not this Nazi one we have now," she was reported as saying by New York newspaper Newsday.
The remark was made on Saturday in an interview conducted by fellow actor Bob Balaban about Sarandon's career that was part of the Hamptons Film Festival.
Newsday said Balaban gently chided Sarandon for the remark but she repeated it.
Sarandon's Hollywood agent did not respond to calls for comment on Monday.
German born Pope Benedict, formerly Joseph Ratzinger, was briefly a member of the Hitler Youth in the early 1940s when membership was compulsory, the Vatican has said. He deserted the military during World War II and has said that as devout Catholics, his parents rejected Nazi ideology.
ADL: No excuse for Nazi analogies
Sarandon, 65, who was raised in New York as a Roman Catholic, is known for her support of causes ranging from hunger and AIDS to opposing the US-led war in Iraq. The "Thelma and Louise" star was appointed a UNICEF Goodwill Ambassador in 1999.
The New York-based Catholic League for Religious and Civil Rights called Sarandon's remark "obscene" and said in a Monday statement that her "ignorance is willful."
The Anti-Defamation League (ADL), which fights anti-Semitism, called on Sarandon to apologize to the Catholic Community.
"Ms. Sarandon may have her differences with the Catholic Church, but that is no excuse for throwing around Nazi analogies. Such words are hateful, vindictive and only serve to diminish the true history and meaning of the Holocaust," the ADL said in a statement.
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