A round cutter-blade of a paper shredder includes a body having a surface, a periphery, and an opening formed therethrough; and at least one triangular shaped knife-edge that is integrally formed with the surface of the body and is turned over the periphery of the body. The cutter-blade can cut broken paper into short fragments, thus raising the secure requirement greatly and reducing the cost due to a reduction of thickness of the round cutter-blade.