The CdS nanoparticles with good crystallinity were prepared by hydrothermal method in microemulsion composed of poly oxyethylene lauryl ether/water/ cyclohexane/butanol. The structure and the size of the nanoparticles were analyzed by TEM and XRD. The UV-Vis optical absorption of the samples was also investigated.The results show that hydrothermal treatment is an effective method to prepare CdS nanoparticles of hexagonal structure at low temperature. The particles were in dimensional uniformity. The diameter of the nanoparticles decreased with the increase of the molar ratio of water to surfactant. The minimum diameter of the nanoparticles prepared in this work was 10 nm. Obvious blue-shift were observed in the UV-Vis absorption.
