Abstract Cadmium sulfide (CdS) nanoparticles have wide application ranging from sensing to solar cells. Therefore it has been a challenge to control the synthesis parameters to obtain the CdS nanoparticles of desired characteristics. Within this study the stabilization of CdS nanoparticles was optimized by varying the concentration of mercapto silane (MS), used as a surfactant. The long term stable dispersions were obtained with 2 and 4 x 10-5 vol% of MS. Both the colloids showed the absorption onset around 485 nm. More detailed structural observation was employed via transmission electron microscopy with selected area electron diffraction detector. The results indicated that CdS nanoparticles are quasispherical with a mean diameter of 3.12 nm and the cubic structure for the nanoparticles stabilized with 2 x 10-5 vol% of MS, whereas the nanoparticles stabilized with 4 x 10-5 vol% of MS had a mean diameter of 4.15 nm and a mixed phase with a hexagonal predominate.