Nanoparticles of copper sulfide have been synthesized by reacting a copper ammonia complex with an equimolar thiourea solution in Triton-X 100/cyclohexane water-in-oil microemulsions. The presence of an exceptionally sharp and blue-shifted peak at 475 ± 2 nm in the UV−vis spectrum reveals the formation of quasi-monodispersed, size-quantized particles. Using absorption spectroscopy, the formation of a chalchocite (Cu2S) phase is inferred. The peak position in the absorption spectra was found to be independent of net micellar water content as well as aging effect. It is attributed to the formation of a Cu(I) thiourea complex on the surface of the particles, which are hydrogen bonded to the polyoxyethylene (POE) chain of Triton-X 100 (TX-100). The role of thiourea in the tailoring of particles to the micellar periphery was confirmed by synthesizing the nanoparticles using other S2- agents like H2S, and Na2S. The role of the POE chain in mediating the adsorption was brought out by carrying out the reaction in microemulsions of POE containing surfactants other than TX-100. The kinetics of agglomeration has been studied and fits well in second-order rate law. A further enhancement in the solution stability of the particles was achieved by means of sodium hexametaphosphate.