CdS nanoparticles were prepared by chemical reaction between some cadmium salt (CdSO4 8/3 H2O and CdNO3 center dot 4H(2)O) and thioacetamide (TAA), in the presence of N-butyl aniline (NBA) as a capping group; and denoted by CdS1 and CdS2 respectively. The structural and morphological properties were studied by powdered X-ray diffraction, transmission and scanning electron microscopy (SEM). The optical properties were studied by the ultraviolet-visible and photoluminescence spectroscopy. The particle sizes were influenced by the nature of the cadmium source. The photoluminescence spectra of the nanopartides show peaks at 630 and 635 nm respectively, which are attributed to the surface defects of the CdS nanoparticles. The dielectric properties of CdS nanoparticles were studied in the temperature range of 25-150 degrees C, and at a single frequency of 1 kHz. The dielectric constant, capacitance and conductivity were found to increase with an increase in temperature at 1 kHz, and opposite behaviour were obtained for the dissipation factor and electrical modulus. The dissipation factor and electrical modulus decreased with an increase in temperature at 1 kHz. The activation energies were obtained from conductivity and capacitance. The activation energies obtained from capacitances were slightly higher than the values obtained from conductivity measurements. The electrical conductivity was found to be dependent on the size of the prepared nanoparticles. (C) 2013 Elsevier Ltd. All rights reserved.