US Edition The Pope believes the Harry Potter books "distort Christianity in the soul", according to two letters published on the internet.
The comments were made to a German author who wrote Harry Potter - Good or Evil? which criticises J K Rowling's best-selling series.
Gabriele Kuby sent Pope Benedict XVI a copy of the book in 2003, when he was still a cardinal, and the pontiff's replies have now been published.
"It is good that you enlighten people about Harry Potter because these are subtle seductions which act unnoticed and by this deeply distort Christianity in the soul before it can grow properly," wrote the Pope.
He thanked Kuby for her "instructive" book, in which she says the Potter series corrupts the hearts of the young, preventing them developing a sense of good and evil.
In a second letter, sent two months later, the Pope "gladly" gave his permission for Kuby to make his judgment public.
The signed letters were published days before Harry Potter and the Half-Blood Prince, the sixth book in the series is published.
The Vatican had previously given the books an apparent seal of approval.
Fr Peter Fleetwood, a senior official, told a press conference in 2003: "I don't think there's anyone in this room who grew up without fairies, magic and angels in their imaginary world."