Spherical aggregates of palladium nanoparticles were produced by stirring palladium(II) acetate with dendritic molecules (i.e., octa(3-aminopropyl)silsesquioxane octahydrochloride, (POSS-NH3+) or the amine-terminated G1.0 poly(amidoamine) dendrimer (G1-NH2)) in methanol at room temperature via self-organized spherical templates of Pd(OAc)(2) and the dendritic molecule. The mixing ratio of the terminal amino groups of the dendritic molecule and palladium ions (Z = [Pd2+]/[-NH2]) affected the formation of the spherical aggregates of palladium nanoparticles. Maximum Z values with no reduction of palladium ions (the solution remained yellow) were 1.0 for POSS-NH3+ and 1.6 for G1-NH2, respectively. TEM observations suggested that the density of the palladium nanoparticles in the aggregates using POSS-NH3+ as a template was higher than that using G1-NH2. From tapping mode atomic force microscopy, shapes of the aggregates using POSS-NH3+ and G1-NH2 were a spherical form and an oval form on plates, respectively. Increasing the. rigidity of the silsesquioxane core of the dendritic molecules increased the stability of the spherical form in the dry state.