Cadmium sulfide (CdS) colloidal nanocrystals have been synthesized by a chemical reaction route. Polyvinyl alcohol was employed to modify the surface of CdS nanocrystals and improved their optical properties. The prepared nanoparticles were characterized using techniques such as x-ray powder diffraction, UV–VIS absorption, and photoluminescence spectroscopy. The prepared sample displays a strong and narrow green emission peak centered at 519 nm that has not been reported before and it is longer than the onset of absorption of for bulk CdS. Several weak emission peaks appeared at wavelengths 490, 506, 521, and 543 nm, too. These two important characteristics of the prepared sample are due to the strong band-edge emission of CdS nanocrystals. The obtained results confirm that the prepared CdS nanocrystals have potential for opto-electronic applications.