This study is concerned with the relationship between wide angle X-ray scattering (WAXS) analysis and physical properties of amorphous polystyrene (PS)-silica (SiO₂) composites. Nanoporous SiO₂ for the fillers was prepared by the hydrothermal reaction and the structures of the composites were examined by WAXS. In their WAXS patterns, two characteristic peaks, inner peak and outer peak, were observed at q ≈ 7 nm⁻¹ and 15 nm⁻¹ corresponding to the intermolecular structure of PS chains and the intramolecular order of benzene rings, respectively. The ratio (I_in⁄I_out=P) in intensity of the inner peak (I_in) to outer peak (I_out) affords the structural parameter to well characterize the intermolecular and intramolecular structures of PS molecules and the P values are observed to change widely from 0.183 to 1.16 depending on the material compositions. The elongation at the break point increases monotonously with increasing P, whereas the yield strength and the Young's modulus decrease with P for P=0.497 or below but remain almost constant for larger P values. The elongation of 4.5% for (PS+MPS) / SiO₂ is enormously larger than those for PS and the other composites, in contrast to a slight decrease of the other two properties relative to those for PS. It is also revealed that a strong interaction works between the COO or COOH groups of maleic anhydride modified polystyrene (MPS) and the OH groups of SiO₂, which makes the PS polymer molecules to stack regularly on SiO₂ nanofillers, leading to control the physical properties of the composites.