A chemical route was used to synthesize highly stable CdS colloidal nanocrystals. Different characterization techniques, such as UV-Vis, photoluminescence, and time-resolved photoluminescence spectroscopy, were used to study the optical properties of synthesized sample. A strong and narrow green emission peak centered at 532 nm with 40-nm full widths at half maximum and 57.2% quantum efficiency was recorded. The absorption cross section at the first absorption peak is about that has not been reported before. Variation in optical properties, such as emission peak intensity and full widths at half maximum of emission peak, was evaluated with various long-term measurements (after 1 year). Obtained results confirm that the prepared CdS nanocrystals can be employed as green source material.