Recently, the wireless location system become an important issue. However, the previous location mechanisms were seldom proposed for locating applications in library. In this paper, we present a smart Book-LOCating System called BLOCS with two location modes using RFID technology - single book mode and book list mode. The single book mode provides users to find the bookshelf containing the desired book which was misplaced. The book list mode offers a corresponding list of the bookshelves and the misplaced books regularly for a librarian to localize all misplaced books in the wrong bookshelves. The simulation results show that the locating accuracies of the single book mode and the book list mode are more than 90% and 85%, respectively.