Yes, it is illegal for libraries to lend pirated books. According to the provisions of China's copyright law, the copyright of a work is enjoyed by the author, and no one else may use it in any way without permission. Pirated books are acts of copyright infringement by unauthorized production, reproduction and dissemination. Borrowing pirated books by the library is not only unauthorized by the author or copyright owner, but also violates the provisions of the copyright law. So it is illegal for libraries to lend pirated books.