【Objective】 Depletion of enrofloxacin and its metabolite in the milk were studied in mastitis cows after a single intramammary dose of 500 mg per quarter.【Method】 Concentration of enrofloxacin and its metabolite ciprofloxacin were determined by high-performance liquid chromatography with fluorescence detector and the concentration-time data were analyzed by statistical moment principle.【Result】 Enrofloxacin and its metabolite ciprofloxacin were all at the peak after 2 hours in the administered quarter.The c...