Abstract: CdTe quantum dots coated with glutathione (GSH) were synthesized in aqueous phase in one step. The synthesized CdTe@GSH quantum dots are water-soluble and stable in aqueous solution. CdTe@GSH processes high quantum yield with controllable fluorescence spectra, which can almost cover the whole range of visible light. CdTe@GSH quantum dots undergo fluorescence quenching in the presence of lead ions, and the quenching efficiency is proportional to lead ion concentration. CdTe@GSH is applied to detecting lead ions of trace quantity in a linear manner within the range between 0.5~500 nmol/L, and the experimental limit of detection is as low as 0.1 nmol/L. Moreover, the detection selectivity is good. The interaction between CdTe@GSH and lead ion is investigated by using electrospray ionization mass spectrometry (ESI-MS) and dynamic light scattering (DLS), which would help us to make a better understand of the quenching mechanism.