A box closure device engages and holds the flaps of a box in their downward closed position. The device is constructed in a general “I” shape such that the top member is parallel and connected to a bottom member by a vertical member. It slides inward between the opposing flaps of a box from one (or either) side of the box with the “I-beam” connecting member of the device fitting in the space between the flaps. The top and bottom members are of sufficient length, width and depth to hold the box closed. The device gains further operative value when promotional or box content labels, business cards, displays, signage, décor, pictures or the like are applied to the surface of the top and/or bottom members of the said device.