Abstract: Through reaction of Cd(Ⅱ), thioglycollic acid (TGA) and alcoholic solution of potassium selenium hydride in an alkaline solution of pH 11, TGA modified CdSe quantum dots were prepared, which were further reacted with Na2S solution to give TGA modified CdSe/CdS quantum dots (QD′s). Based on the fluorescence quenching action of the antibiotic sparfloxacin (SPFX) on the QD′s, the CdSe/CdS QD′s were used as fluorescence probe for determination of SPFX, and principle of this fluorescence quenching reaction was studied by fluorescence spectrometry and UV-spectrometry. It was found that in a PBS of pH 6.47 and keeping the concentration of CdSe/CdS QD′s at 2.5×10-4mol·L-1, linear relationship between the magnitude of fluorescence quenching and mass concentration of SPFX was kept in the range of 0.5-30 mg·L-1, with detection limit (3s/k) of 0.14 mg·L-1. In the analysis of SPFX tablets by the present method, values of SPFX contents found were in consistency with the labelled value. SPFX was also determined in milk samples by this method, and using milk sample as matrix, recovery of the method was tested by standard addition method, values of recovery found were in the range of 95.3%-106.8%.