Abstract: The pharmacokinetics and residues of ciprofloxacin hydrochloride in the milk were investigated in 5 cows suffered from endometritis following singleintrauterine administration at the dosage of 2.5 per cow. Blood and milk were sampled at different intervals after administration and ciprofloxacin hydrochloride concentrations were determined by RP-HPLC method with a fluorescent detector. Difloxacin was used as intra-standard. The concentrationtime data were analyzed with MCPKP program. The ciprofloxacin hydrochloride concentrationtime data were fitted to a twocompartment open model with first order absorption in two cows suffered from endometritis after singleintrauterus. The main pharmacokinetics parameters were as follow: T _1/2α 1.26 h, T_1/2β9.2 h, AUC 28.336 mg/L·h, β 0.3571 h^-1. The ciprofloxacin hydrochloride concentration-time data were fitted to a three-compartment open model with nonabsorption in other three cows. The main pharmacokinetics parameters were as follow: T _1/2α0.916 h, T_1/2β49.20 h, AUC 7.6296 mg/L·h,Clβ 1.582 L/kg·h, β 0.642 h^-1. The results showed that ciprofloxaxin hydrochloride was absorbed fast and distributed extensively, but it was eliminated slowly in the blood after singleintrauterine administration.