An aerosol size-selective impactor for reducing particle bounce includes a main structure, a buffering layer, and a dehydration preventing layer. This main structure with an inlet and an outlet has a central channel and a receiving cavity. There are many nozzles in the inlet. The buffering layer is filled in the receiving cavity. The dehydration preventing layer is coated on the buffering layer for reducing the dehydration of water contained in the buffering layer. So, this invention utilizes the design of the receiving cavity to receive both layers. Its accuracy is high. Its sampling time lasts longer. It can endure vibrations. This invention can yield the particle bounce effect with lower cost. And, its application scope is wide.