The surface of waste ground rubber tire (WGRT) powder has been modified with by allylamine via an ultraviolet (UV) treatment. The degree of grafting of the modified-WRGT are confirmed by the Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis, and surface energy measurements. And then they incorporated into the polypropylene (PP) matrix. The effects of UV radiation time, WGRT loading, and allylamine concentration on the mechanical properties of the composites are measured. Mechanical properties are influenced as a function of UV radiation time, WGRT loading, and allylamine concentrations. The chemical interactions between grafted WGRT and PP matrix are investigated by X-ray diffraction and FTIR. They show change of the crystallinity of the PP and the chemical reaction between WGRT and the PP. POLYM. ENG. SCI., 49:168-176, 2009. (C) 2008 Society of Plastics Engineers