She's managed to stop the Russian book about a girl wizard called Tanya Grotter because she says it copies her best-selling novels.
The book, called The Magic Double Bass by Dmitry Yemets, is all about Tanya Grotter and her days at a witch school called Abracadabra.
Evil force
She's an orphan, has a strange mark on her face and has magical powers.
Judges at a court in Amsterdam agreed with JK that it was too similar to Harry Potter and shouldn't be published there.
The decision means 7,000 copies of the book will now be stopped.
Although Byblos, the Dutch publishers of the book, do have the right to appeal the decision.
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