The water-soluble CdTe /ZnS core-shell quantum dots（QDs） were synthesized using thioglycolic acid（TGA） as stabilizer．It was found there is an appreciable over lap between the emission spectrum of CdTe /ZnS QDs and the absorption spectrum of malachite green（MG）.Moreover，the interaction（mainly the electrostatic force） between the electronegative CdTe QDs and cation dye MG can draw them close.Thus，the fluorescence resonance energy transfer（FRET） system was constructed between CdTe /ZnS QDs（donor） and MG（acceptor）.Based on this FRET system，a sensitive method for the determination of MG was developed.Effects of experimental conditions were investigated.The optimal conditions were as follows：buffer:pH 8.0 Tris-HCl solution，concentration of quantum dots：1.6×10-4 mol/L，reaction time:20 min，reaction temperature：30 ℃.Under the optimal conditions，a good linearity was obtained between the quenched fluorescence intensity of CdTe /ZnS QDs and concentration of MG in the range of 0.048-3.2 μmol/L.The correlation coefficient was 0.999 3 and the limit of detection（3σ） was 0.015 8 μmol/L.The proposed method was successfully applied in the determination of MG in water samples with spiked recoveries of 99.3%-102 %.Furthermore，the possible mechanism of interaction between CdTe/ZnS QDs and MG was discussed.