Polystyrene(PS)/triphenyl phosphate(TPP) composites were prepared by both suspension polymerization and melt extrusion, and a comparative study of the flame retardance and mechanical properties was carried out. The results showed that suspension polymerization was a better technique than melt extrusion for obtaining good dispersity of the PS/TPP composite. The TPP nanoparticles, which were approximately 50 nm in size, were homogenously and uniformly dispersed in the PS matrix by suspension polymerization in one-step. However, the PS/TPP composite was partially agglomerated, exhibiting irregularly shaped micron-scale particles as a result of melt extrusion. In contrast to the melt extrusion, the limited oxygen index(LOI) of the PS/TPP nanocomposite by suspension polymerization increased to 22.6% from 21.8%, and time to ignition(TTI) increased by 12.3%, the peak heat release rate(PHRR) decreased by 8.5%, and the total heat release(THR) decreased by 11.0%. The mechanical properties of the PS/TPP nanocomposite by suspension polymerization also increased. The tensile strength, elongation at break, and flexural strength increased by 36.4%, 8.5%, and 108%, respectively. Polystyrene (PS) / triphenyl phosphate (TPP) composites were prepared by both suspension polymerization and melt extrusion, and a comparative study of the flame retardance and mechanical properties was carried out. The results showed that suspension polymerization was a better technique than melt extrusion for Obtaining good dispersity of the PS / TPP composite. The TPP nanoparticles, which were approximately 50 nm in size, were homogenously and uniformly dispersed in the PS matrix by suspension polymerization in one-step. However, the PS / TPP composite was partially agglomerated, exhibiting irregularly shaped micron-scale particles as a result of melt extrusion. the limited oxygen index (LOI) of the PS / TPP nanocomposite by suspension polymerization increased to 22.6% from 21.8%, and time to ignition ( TTI) increased by 12.3%, the peak heat release rate (PHRR) decreased by 8.5%, and the total heat release (THR) decreased by 11.0%. The mechanical properties of the PS / TPP nanocomposite by suspension polymerization also increased. The tensile strength, elongation at break, and flexural strength increased by 36.4%, 8.5%, and 108%, respectively.