The polypropylene/silica sand powder polymer composite materials were fabricated by using the melt mixing method in a Haake internal mixer at 190 o C. The influence of size and BCSi content on melt rheology, mechanical properties, and structural morphology was investigated. The results show the torque of the PP/BCSi composite material decreased as the BCSi content increased from 10 to 30% wt, but then increased at 40% and 50% wt. The tensile strength, elongation, and impact strength of the PP/BCSi composite were lower than that of PP, but the hardness was higher. When comparing PP/BCSi composites made with silica sand powder modified with steric acid (BCSiA) to unmodified (BCSi), those made with BCSiA had higher mechanical properties. By studying SEM images of the composite surface, we observed that BCSiA increased phase interaction, adhesion, and dispersibility of BCSi into the PP plastic substrate.