We report the synthesis and characterization of a low-cost high-quality CdS quantum dots (QDs).The synthesis was performed in aqueous system. The aqueous CdS colloidal solution was prepared using thioglycollic acid as a capping agent. Zetasizer Nano ZS (Malvern, UK) was employed to characterize the partical size of CdS QDs. The UV-vis and photoluminescence (PL) spectra of samples were systematically characterized (the full width at half maximum was 38 nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 68.5 %. The fluorescence intensity was enhanced by copper (II). The relative fluorescence intensity was linear to copper (II) concentration over the range 4.0 ×10-6 - 2.8×10-5 g mL-1. The regression equation was ΔIF= 59.07+ 90.57c (c / μg mL-1). The highly monodispersed CdS QDs could be used in many fields.