Cattle bone-based hydroxyapatite (HA) powders were prepared. Three types of silane coupling agents, i.e. γ-aminopropyl triethoxysilane (APES), methyl trimethoxysilane (MTMS), and γ-glycidoxypropyl trimethoxysilane (GPMS) were used to modify the HA surface. Untreated HA powders and silane-treated HA powders were utilized to produce HA/polypropylene (PP) composites containing a 60% (w/w) of HA content. Effect of filler surface modification on properties of HA/PP composites were investigated. The results suggested that treating HA surface with a silane coupling agent enhances interaction at HA-PP interface. Among the silane coupling agents used in this study, APES is, on average, the most effective agent for enhancing stiffness of HA/PP composites.