Former pope Benedict has acknowledged he was a better professor than a leader, revealing in a new book that he sometimes struggled to take decisions during his time in charge of the scandal-plagued Vatican.

However, in a book-long interview, the German-born Benedict, who is now 89, said he did not regard his eight-year stint as head of the world's 1.2 billion Roman Catholics as a failure.

Benedict stepped down as pope in 2013, becoming the first pontiff in 600 years to resign, leaving behind a Church tainted with scandals and snarled by mismanagement.

In excerpts of the new book published yesterday by Italian newspaper Corriere della Sera, Benedict said he had not been comfortable in a leadership role.

"One of my weak points is perhaps a lack of resolve in governing and in decision taking. In reality I am more of a professor, a person who reflects and meditates on spiritual questions," Benedict said in the book, "The Last Conversations", by German journalist Peter Seewald.

"Practical government is not my strong point and that is certainly a weakness. But I cannot see myself as a failure."

Benedict described difficult moments including scandals around child sex abuse by priests, which he was accused of not doing enough to stop, and over his lifting the excommunication of a Holocaust-denying bishop.

He also mentioned the "Vatileaks" case in which his butler leaked documents alleging corruption at the Vatican, but said overall there had been a "positive movement" during his papacy.

Benedict, who lives in the grounds of the Vatican, revealed that the election of Argentinian Cardinal Jorge Mario Bergoglio as Pope Francis had come as a huge surprise to him.

But Benedict said the elevation of Francis, whom he described as experienced at "practical reform" unlike himself, showed the Church was moving forward.

Anger at the dysfunctional state the Vatican had fallen into in 2013 was one factor in the decision to choose a non-European pope for the first time in nearly 1,300 years.