But she also said that anyone hoping to get clues about the fifth book from the film will be disappointed.
JK said she loved the film's Quidditch sequences.
"I couldn't imagine how they were going to do it, but they have, and it looks so real."
The movie has its world premiere on Sunday and opens across the UK on 16 November.
You can read the full interview with JK Rowling by going to the link on the right.