US nanocrystals have been prepared successfully using successive ionic layer adsorption and reaction (SILAR) method at room temperature (26 degrees C) in polymer matrix. Gelatin coated on ordinary glass slide used as a matrix substrate, the nanocrystals were prepared using cadmium acetate as a cadmium ion source and sodium sulfure as a sulfure ion source. To obtain good quality of US nanocrystals the preparative conditions such as concentration, pH and temperature of solutions were optimized. Nanocrystals formed in gelatin matrix were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) that the structure is polycrystalline with cubic structure, of about 20 nm which aggregated in the form of polydispersive nanoclusters with sizes in the range of 10-80 nm. Optical absorption and transition study shows a blue shift in band gap energy and this shift is decrease with number of cycles. The energy dispersive X-ray analysis (EDAX) reveals the average atomic percentage of Cd:S was 59:41, showing that the preparation are almost stoichiometric. (C) 2007 Elsevier B.V. All rights reserved.