Abstract:A new synchronous fluorimetric method was developed for the determination of trace ceftiofur in pig muscel and kidney， which was based on the stronger fluorescence intensity of ceftiofur's degradation product in the alkaline condition and the fluorescence intensity was improved by Tween -80.The degradation conditions （such as heating time，the volume and concentration of sodium hydroxide） were optimized. The effect of types and amounts of surface active agent and buffer on the fluorescence intensity of degradation product was dis－ cussed. The results showed that the optimum conditions were 4 mL 2.0 mol/L sodium hydroxide， heating time of 150 min， the buffer of 3 mL citric acid-sodium citrate（pH 4.2） and 6 mL Tween-80 solution（0.023 3 mol/L）. The standard and sample solutions were added into 1cm fluorescence cuvette， Synchronous fluorescence spec－ trums were scanned from 415 nm to 550 nm， △λ was 85 nm and then the fluorescence intensities were read at 440 nm. The proteins in food sample were precipitaded by acetonitrile. The results showed that in the range of 0.625 μg/mL-62.5 μg/mL， the concentration of ceftiofur and the fluorescence intensity of its degradation prod－ uct had a good linearity with the correlation coefficients of 0.999 3.The detection limit was 270 μg/kg. At spiked levels of 144 μg/kg to 2 160 μg/kg， the sample recovery ranges from 85.09 % to 87.83 %， the relative standard deviation was 0.93 % to1.54 %（n=3）. The results demonstrated that the new method proposed in this work could be used for the determination of residue ceftiofur in animal food.