Cd1-xZnxS (0≤x≤1) alloy quantum dots (QDs) were synthesized via coprecipitation method using cetyltrimethyl ammonium bromide (CTAB) as a capping material. Elemental composition of the investigated samples was determined by the energy dispersive x-ray spectroscopy (EDX). X-ray powder diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to characterize the crystalline structure, particle size and morphology. XRD analysis indicated that the as synthesized nanomaterials, except for ZnS, have a mixture of cubical and hexagonal phases. The percentage of the hexagonal phase was very small. ZnS nanocrystal has a cubical structure. The particle size and the lattice constant decreased with the increase of Zn content. HRTEM data showed the presence of QDs and confirmed the XRD results. Ultraviolet-visible (UV-vis) absorption spectroscopy was employed to study the optical properties. Absorption band edges showed blue-shift systematically with the increase of Zn content. The results are interpreted in terms of the quantum-size confinement effect. Measurements of XRD and UV-vis absorption spectra under different annealing temperatures up to 400°C were performed. The annealed compositions showed mixture of cubical and hexagonal crystal structure. Tendency for phase transformation, from cubic to hexagonal upon annealing were observed. The degree of tendency for phase transformation increased with the decrease of Zn content and the increase of the annealing temperature. Particle sizes were increased with increasing the annealing temperature. UV- vis absorption spectra exhibited red-shift systematically with the increase of the annealing temperature. The values of the optical band gap energies decreased with increasing annealing temperature.