The timeline of all of her published works is such:
1.) Harry Potter and the Philosopher's Stone
2.) Harry Potter and the Chamber of Secrets
3.) Harry Potter and the Prisoner of Azkaban
4.) Harry Potter and the Goblet of Fire
5 and 6.) Quidditch Through the Ages and Fantastic Beasts and
Where to Find Them
7.) Harry Potter and the Order of the Phoenix
8.) Harry Potter and the Half-Blood Prince
9.) Harry Potter and the Deathly Hallows
10.) The Taled of Beedle the Bard
The answer then, to your question is Harry Potter and the
Half-Blood Prince.