An auxiliary unit of paper shredder cutting tools is installed on cutting tools of a paper shredder. The auxiliary unit is formed by two L-shape plates located between two neighboring blades, an arc-shape hole at an end of each L-shape plate is hooked on a cutting bar of the cutting tool, and a through-hole of each L-shape plate provides for a support rod to be transfixed, so as to stably fix paper guides, the cutting bars and the blades. Therefore, the paper guides, the cutting bars and the blades can be prevented from getting loose or stretched open to damage the paper shredder or result in noise or even an imperfect shredding effect.