Functionalized reverse micelles are used to control the size of silver sulfide, Ag 2 S , nanosize particles. The size of the crystallites varies linearly with the water content from 2 to 10 nm. The particles have been coated with dodecanethiol and extracted from micelles. The size of the particles dispersed in heptane has been determined by small-angles x-ray scattering (SAXS) experiments and compared to those obtained by transmission electron microscopy (TEM). A good agreement between results is obtained by these two techniques. A drop of particles previously dispersed in heptane is dried on a carbon grill. A network of the particles forming monolayers of crystallites in a hexagonal distribution appears.