Nanostructure CdS particles have been successfully prepared by chemical reaction of cadmium acetate (C4H6CdO4.2H 2O) as a Cd2+ ion source and thiourea (H 2NCSNH2) as a S2- ion source in aqueous media with inducement ultrasonic irradiation at room temperature and normal laboratory conditions. This simple and one step preparation can be considered as a green synthesis. The obtained particles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and UV-Vis spectrophotometer. XRD pattern reveals that the CdS nanoparticles formed are highly pure and are crystalline in nature with cubic structure. SEM images shows that the product consists of spherical nanocrystallites of about 20nm which aggregated in the form of polydispersive. Energy dispersive X-ray analysis (EDAX) shows that the proportion of cadmium to sulfur is neatr to Cd:S=1:1, showing that the product is almost stoichiometric. Optical measurements indicate a direct band gap of about 4.69 eV. There was observed a blue shift of about 2.29 eV, in comparison to its bulk value due to quantum confinement effects of electrons and holes.