A kind of novel gold (Au)/hydroxylated poly (styrene-b-butadiene-b-styrene) triblock copolymer (HO-SBS) composite nanoparticles was synthesized by reduction of tetrachloroaurate ions in HO-SBS micelle. The Au-HO-SBS composite nanoparticles are composed by gold core about 35 nm in diameter and polymer shell about 7 nm in thickness. Formation of the Au/HO-SBS nanoparticles is indentified by infrared (IR) and UV-visible absorption spectroscopies. Transmission electron microscopy (TEM) result shows that the composite nanoparticles tend to aggregate into an ordered hexagonal array on carbon-coated grid.