The results of the studies on the preparation and stability of thiophenol-capped US nanoparticles prepared by a non-aqueous chemical method are reported. Solutions of cadmium acetate and sodium sulphide were taken as the precursors and thiophenol was used as a capping agent to control the growth and also to prevent flocculation of the synthesized particles. The synthesized US nanoparticles were characterized by the optical absorption and X-ray diffraction (XRD) studies. The blue shift of the optical absorption edge indicated the formation of particles in the nanometer size regime. The particle sizes were estimated from the band gap values obtained from the optical absorption spectra using effective mass approximation (EMA). The US powder sample was used for the X-ray Diffraction studies. Broadening of the diffraction peaks with an increase in the stabilizer concentration also suggests the decrease in particle size with increase in the stabilizer concentration. Particle sizes calculated from the X-ray diffraction studies agree fairly well with those estimated from the optical absorption studies. The particle size could be conveniently controlled by adjusting the concentration of the stabilizer. X-ray diffraction studies were also carried out at higher temperatures. Particle size did not change with temperature as indicated by XRD. Stability of the synthesized nanoparticles was studied by recording the optical absorption spectra for 45 days. A change in particle size was observed at lower stabilizer concentrations for the first few days. But at higher stabilizer concentrations there was no change in particle size with time. (c) 2006 Elsevier B.V. All rights reserved.