Spherical bridged polysilsesquioxane (BPS) nanoparticles were prepared by the hydrolysis and condensation reaction of urethane-based BPS monomer made from 1, 4-butanediol and 3-(triethoxysily)propyl isocyanate. Polydopamine (PDA) was coated on the surfaces of BPS by the self-polymerization of dopamine under pure oxygen at room temperature. To create aggregates of Pd nanoparticles on PDA-coated BPS, polyhedral oligomeric silsesquioxane (POSS-NH3+) as a cross-linker was incorporated on the surfaces of PDA-coated BPS. Aggregates of Pd nanoparticles were densely produced on the surfaces of PDA-coated BPS by the mixing of POSS/PDA-coated BPS and palladium (?) acetate in a methanol solution.