To enhance the compatibility of polypropylene (PP) with sericite-tridymite-cristobalite (STC), polypropylene was irradiated by low-energy ultraviolet (UV) irradiation within 2.5 h to introduce the oxygen-containing groups onto the PP chains. From blending the W-irradiated polypropylene with STC, the effects of the compatibility on the structure and properties of PP-STC blends could be investigated by differential scanning calorimetry, thermogravimetry, thermomechanical analysis, wide-angle X-ray diffraction, scanning electron microscopy, mechanical properties, and melt index measurements. The experimental results show that for the UV-irradiated PP-STC blends, the degree of crystallinity is smaller than those with an unirradiated PP-STC blend, the thermal degradation temperatures are increased and the thermal stability is improved. Furthermore, with the UV time varying from 0 to 2.5 h, the melt index increases from 2.73 to 3.39 g/10 min, and the mechanical properties improve, exhibiting stiffening and toughening effects. Also a toughened morphology can be observed because of the enhanced interaction between W-irradiated polypropylene and STC.