Shape- and size-controlled syntheses of metal nanoparticles have been achieved by galvanic displacement reaction between an aqueous solution of metal salt and Cu foil substrate. In particular, cubic and spheric nanciparticles of Pt (Au) with a fairly narrow size distribution were produced by reacting K2PtCI4 (HAUC14) with a Cu foil in an aqueous medium with and without CUC12 under different reaction conditions (e.g., different concentrations and reaction times). In conjunction with the substrate-enhanced electroless deposition (SEED) technique (Qu, L.; Dai, L. J. Am. Chem. Soc. 2005, 127,10806), the shape/size-control led syntheses have been successfully exploited to site-selectively deposit these metal nanoparticles onto the outerwall, innerwall, or end-tip of carbon nanotubes (CNTs). Asymmetric sidewall modification by attaching the innerwall and outerwall of CNTs with metal nanoparticles of different shapes was also achieved. Furthermore, it was demonstrated that the nanotube-supported Pt nanoparticles could be converted into hollow Au nanoboxes by galvanic displacement of Pt with Au. These CNT-supported metal nanoparticles were shown to possess interesting optical and electrocatalytic properties.