Hydroxyapatite (HA) particles were modified by in situ polymerization of styrene (St) and in situ copolymerization of vinyltriethoxylsilane (VTES) and St, respectively. The modified HA particles were compounded with polystyrene (PS) and high impact polystyrene (HIPS). The effects of surface modifications of HA on interfacial adhesion, strengthening, toughening and wear- resistance of PS/HA and HIPS/HA composites were investigated. The results showed that the PS macromolecules covered the HA surface via physical interaction during in situ polymerization of styrene, whilst the PS chains were grafted on the surface of HA particles during in situ copolymerization of VTES and St. The weight-average molecular weights of PS chains on the HA surface during in situ polymerization and copolymerization exceeded 300,000. Therefore, the PS segments which covered via physical interaction, and those that were chemically grafted on, the HA surface enhanced the interfacial adhesion between HA particles and polymer matrix, such as PS and HIPS, and improved the tensile strength and impact toughness values of the PS/HA and HIPS/HA composites. As a consequence of the strengthening and toughening imparted by the modified HA particles to HIPS and PS, the abrasive wear resistance of the HIPS/HA and PS/HA composites was improved.