The comments came in an exchange of letters between then-Cardinal Joseph Ratzinger and Gabriele Kuby (search), a Bavarian-based Roman Catholic sociologist who penned a book criticizing J.K. Rowling's blockbusters.
In a letter dated March 7, 2003, the text of which could be seen Thursday on Kuby's Web site, Ratzinger thanked her for sending him a copy of "your informative book."
"It is good that you are throwing light on Harry Potter, because these are subtle seductions that work imperceptibly, and because of that deeply, and erode Christianity in the soul before it can even grow properly," the letter added.
The Vatican had no comment, noting that the pontiff — a Bavarian native — and his secretary were away on vacation.
Kuby argues in her book, "Harry Potter — Good or Evil," that the Potter novels blur the boundaries between good and evil and impair young readers' ability to distinguish between the two. She also asserts that they glorify the world of witches and magicians at the expense of the human world.
Christians in the United States have made similar criticisms.
Kuby said Thursday that she sent her book to Ratzinger — then the Vatican's doctrinal watchdog — after he commented favorably on an earlier book she wrote, "My Way to Mary."
In an e-mailed response to questions, she said she did not correspond with Ratzinger about Potter again after seeking his permission to cite his judgment later in 2003.
Ratzinger wrote on May 27 that year that "I gladly permit you to cite my opinion on Harry Potter," according to Kuby.
Rowling's sixth Potter book, "Harry Potter and the Half-Blood Prince," (search) is due out Saturday.