CdS colloidal quantum dots are prepared with different reactant ratio of CdO and Sulfur. Under the ratio of 1:3 molar amounts, there was no difference on the absorption and photoluminescence spectra, which means that similar size(~3.6nm) of quantum dots formed with no regard to the reactant ratios. However, at the ratio of 1:9 we could not observe a meaningful absorption spectra. It also showed very different PL spectra, which implies the formation of different materials.