Five hundred tickets are up for grabs for the event on 15 August. To apply, fans must fill in a form from the website of JK's publishers Bloomsbury.
Fans have until 20 July to apply - at www.bloomsbury.com - and the winners will be informed by 23 July.
JK will give readings from her most recent book, Order Of The Phoenix, and answer questions from fans.
The event celebrates the publication of OOTP in paperback.
"I am looking forward to this event very much because there will be a relatively small audience, which means I can see faces and take questions directly from the fans," said JK.
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