Herein, a yellow cadmium sulfide (CdS) QDs solution was obtained via the reaction of sodium sulfide (Na2S) with Cd-coordinated chitosan (Cd 2+ /CTS) solution under stirring at mild temperature (90 o C). The prepared material, i.e., CdS/CTS QDs, was dried via the freeze-drying method. CdS/CTS QDs were analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution TEM image (HR-TEM), scanning TEM (STEM), Energy-dispersive X-ray (EDX) analysis/mapping, Fourier transforms infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherm, diffuse reflectance spectroscopy (DRS), and thermogravimetric analysis (TGA). It was applied for the chemosensing of heavy metal ions. It showed higher selectivity toward copper (Cu 2+ ) ions than other metal ions. The interaction mechanism between CdS/CTS QDs and Cu 2+ ions was supported with experimental data such as TEM, HR-TEM, STEM, EDX analysis/mapping, DRS, FT-IR, and XPS.