The feasibility of reusing the recycled glass fibers (RGF) from nonmetals of waste printed circuit boards in polypropylene (PP) composites is studied by mechanical properties, vicat softening temperature and heat distortion temperature. The influence of RGF on reinforcing mechanism of the composites is watched under scanning electron microscopy (SEM) in situ tensile test. The results show that the mechanical and thermal properties of the RGF/PP composites can be significantly improved by adding the RGF into PP. In situ SEM observation results show that the RGF are the excellent supporting bodies and can effectively lead to mass microcracks. Crack initiation, propagation, and fiber breakage dissipate tremendous energy. Therefore, the mechanical properties are reinforced. All the above results indicate that the reuse of RGF in the PP composites represents a promising way for closing the recycling loop and realizing the high added value utilization. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2914-2920, 2010