Three-dimensional (3D) assemblies of metal nanoparticles are promising materials for plasmonic materials. Metal nanoparticles have unique surface plasmon resonances, ranging from ultraviolet to visible light wavelengths, depending on their metal species, size, and shape. The arrangements and spacing of the nanoparticles also strongly affect the plasmonic properties. The microphase separation of block copolymers can create a nanoscopic periodic structure, where metal nanoparticle assemblies are arranged along the microphase separation structure. In this paper, we construct 3D Au nanopartide assemblies embedded in the microphase separation structures of confined block copolymers, in the pores of inverse opals. Polymer-stabilized Au nanoparticles were synthesized, and submicrometer poly(styrene) ;(PS) colloidal crystals were prepared using a simple coating method, After molding a PS colloidal crystal with poly(vinyl alcohol) (PVA), block copolymers and Au nanoparticles were introduced into the PVA inverse opal from solution. The inner nanostructures were analyzed by transmission electron microscopy (TEM).