Which novel is the longest of J.K. Rowling’s seven Harry Potter books in the UK editions?

Harry Potter and the Order of the Phoenix is the longest of J.K. Rowling’s seven Harry Potter books in the UK editions. Its Bloomsbury hardback edition contains 766 pages.

Published on 21 June 2003, the fifth novel follows Harry’s growing conflict with the Ministry of Magic and the return of Lord Voldemort. At Hogwarts, Dolores Umbridge restricts practical Defence Against the Dark Arts teaching, prompting Harry and other students to form Dumbledore’s Army.

Page-count comparisons can vary by edition, language, typography, and format. The US hardcover is commonly listed at 870 pages, while the UK hardback has 766 pages. The important comparison is therefore tied to the edition specified: among the original UK editions, Order of the Phoenix is the longest.