High-Fluorescence Mn-doped ZnS quantum dots ( QDs) capped with L-Cysteine (L-Cys) were prepared in the aqueous were presented in this paper. The influences of the pH, the doped-quantity of Mn2+ and the storage time on the PL emission of quantum dots were studied. The samples were characterized by means of ultraviolet-visible absorption spectrometry (UV-vis), photoluminescence (PL) emission and infrared spectrometry (FTIR). The results showed that the fluorescence intensity reached the maximum when the pH was 10, the doped-quantity of Mn2+ was 3% and the storage time was about 7 days. The solubility of the quantum dots in the water was excellent. Because of these advantages, it can be used in biological fields, such as biomarkers, cell imaging, and sensor and so on.