High densified CdS polycrystalline microspheres have been successfully synthesized by the hydrothermal method with high gravity field using CdCl2 center dot 2.5H(2)O and Na2S2O3 as precursors in the aqueous solution-chlorobenzene system at 100-140 degrees C for 0.5 h. The products were characterized by field-emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), powder X-ray diffraction (XRD), UV-vis, and IR spectra. It was found that the as-prepared products were the spherical CdS particles, which were self-assembled by the crystallites with the size of 4-25 nm. The formation process of the spherical CdS particles consists of the growth step of CdS crystallites in aqueous solution followed by the self-assembled stage of CdS crystallites in the interface between aqueous solution and chlorobenzene. The smaller the size of CdS crystallites is, the bigger the density of the formed CdS particles is. The size of CdS crystallites was related to the reaction temperature, reaction time, precursor concentration and relative centrifugal field. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.