The influence of oxygen plasma induced vapor phase grafting of acrylic acid on the surface properties of poly (p-phenylene benzobisoxazole) (PBO) fibers and interfacial adhesion with epoxy resin matrix were investigated in this paper. After treatment, XRD results show that the average crystal size slightly decreased from 9.85nm to 9.12nm. AFM scanning graphs indicate that the surface roughness of PBO fibers increased significantly. XPS spectra show the percentage content of polar oxygen-containing functional groups obviously increased after modification. The interfacial shear strength between treated PBO fibers and epoxy resin matrix increase by 55%, while the single-filament tensile strength slightly decrease by 8%.