A simple procedure has been developed to prepare thiol-derivatized nanoparticles of metals. The procedure involves the transfer of well-characterized metal hydrosols to a hydrocarbon medium containing the thiol. Thiol-derivatized nanoparticles Au, Ag, and Pt of near spherical shape forming nanocrystalline arrays have been characterized by X-ray diffraction, transmission electron microscopy (TEM), and other techniques. Thiol-derivatized Au particles of mean diameters of 1.0, 2.1, and 4.2 nm from nanocrystalline arrays show characteristic X-ray diffraction patterns. The nanoparticles exhibit Moiré fringes when deposited on a flake of MoSe2, showing that each particle is in itself crystalline. Besides spherical nanoparticles, thiol-derivatized particles of other shapes have been prepared, hexagonal Pt nanoparticles being particularly novel. Scanning tunneling microscopy images not only confirm the size and shape of nanoparticles revealed by TEM, but also show evidence for thiol molecules on the surface.