New organometallic salts were synthesized in aqueous solution and were used as precursors for the functionalization of carbon nanotubes (CNT) by metallic nanoparticles. The precursors were obtained by reaction between HAuCl, (NH)PtCl, (NH)PdCl, or (NH)RhCl with cetyltrimethylammonium bromide (CTAB). The as-obtained (CTA)MeCl salts (with Me = Au, Pt, Pd, Rh) were characterized by Fourier-transform infra-red (FTIR) spectroscopy, H nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis. These precursors were then used to synthesize metallic nanoparticles of Au, Pt, Pd, and Rh over multiwalled carbon nanotubes (MWCNT). Characterization by scanning transmission electron microscopy (STEM) and thermogravimetric analysis under air reveals that the CNT-supported catalysts exhibit high loading and good dispersion of the metallic nanoparticles with small average particle sizes. The present preparation procedure therefore allows obtaining high densities of small metallic nanoparticles at the surface of MWCNT.