Nanoparticles of improved stability against long-term aggregation were prepared using poly(styrene)b-poly(2-vinylpyridine) (PS-b-P2VP) star-block copolymer architectures. The star-block copolymers, physically resembling diblock copolymer micelles, were synthesized by anionic polymerization and coupling with ethylene glycol dimethacrylate. They contain P2VP core segments that facilitated conversion of HAuCl4 to single gold nanoparticles. The size distribution and long-term stability against aggregation of the gold nanoparticles were investigated both as solution and as films. UV-vis spectroscopy and transmission electron microscope images reveal long-term stability against aggregation up to 1 month.