A sensitive fluorescence biosensor for determining sparfloxacin (SPF) based on the electron transfer mechanism and the fluorescence quenching effect of SPF to cadmium telluride quantum dots (CdTe QDs) was developed. The mechanism of the interaction between SPF and CdTe QDs was investigated by UV/Vis absorption and fluorescence spectroscopy. The biosensor could be used for the determination of SPF with a high sensitivity. Under optimum conditions, the linear range was from 0.28 to 40 mu g SPF ml(-1) with a correlation coefficient of 0.9983, and the detection limit (3 delta/k) was 83.7 ng SPF ml(-1). Furthermore, this method has been applied to the determination of SPF in the synthetic environmental water samples and the spiked human serum samples with good results.