A versatile packaging box for products, which can be folded into a book cover or a sealing sleeve for the contained book, is disclosed. On its front, rear, left, and right vertical panels, a folding line whose position is adapted to the thickness of the contained book is respectively provided. The front, rear, left, and right vertical panels are provided with foldable end panels. After the end panel is folded, the length of the rest part of the height of the left vertical panel is equal to the length of the front cover of said book, and so is the length of the rest part of the height of the right vertical panel, either. When the end panel is folded onto the inner side of the rear vertical panel, the length of the rest part of the height of the rear vertical panel is equal to the width of the front cover of said book.; When the end panel is folded onto the inner side of the front vertical panel, the length of the rest part of the height of the front vertical panel is also equal to the width of the front cover of said book. Said box has the advantages as follows: making full use of the used packaging box, beautifying & protecting the contained book, and reducing the wastes.