Abstract: A packing box made by folding a sheet material, and comprised of a body portion, a bottom portion at one end, and a cap portion at an opposite end, said cap portion being folded into four cap panels and four end panels, said end panels being folded up outwards and overlapped on said cap panels respectively, said cap panels being cut into four blocking panels, wherein twisting said cap panels and end panels downwards in one direction causes said blocking panels to be intersected and overlapped one another in blocking up the top opening of the packing box; twisting said cap panels and end panels upwards in an opposite direction causes said blocking panels to be separated from one another permitting said top opening to be opened.