The interaction of a water-soluble ABA type of dumbbell-shaped polyethyleniminated copolymers (D400(EI)(8)) with H2PtCl6 in aqueous medium is studied by means of UV-visible absorption spectra, dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM). From TEM images of the stained polymer, it is evident that the spherical and well-structured polymer micelles are formed by the introduction Of H2PtCl6, and totally nonstructured micelles are formed from D400(EI)S itself. These findings coincide with the results obtained from DLS measurements, where the narrowly distributed polymer aggregates are remarkably observed. Moreover, it is directly evidenced from TEM that the reduced Pt(0) nanoparticles are embedded in the polyethylenimine (PEI) block at the exterior of micelles, whereas the polyoxypropylene (PPO) block is surrounded by the PEI block. Additionally, the resulting Pt(0) colloids are very stable for at least 4 months. (c) 2005 Elsevier Inc. All rights reserved.