The study established a method to analyze clorsulon concentration in sheep plasma by reverse phase-high performance liquid chromatography(RP-HPLC)with an internal-standard.In plasma,clorsulon concentration within 0.01-1.0μgmL-1 and 1.0-20μgmL-1 ranges had a good linear relationship(R= 0.9991,0.9958). The average recovery of the method was 98.11±3.52%. The relative standard deviation(RSD)s% of within-day and between-day assays were less than 7 and 8% respectively. After giving clorsulon to sheep by intravenous(i.v.)or subcutaneous(s.c.)routes at a single dose of 4mgkg-1,drug concentration-time data in plasma were both fitted to a two-compartment open model. The main pharmacokinetic parameters were: 1)i.v. administration: T1/2β = 10.04 ± 0.819 h,area under the concentration versus time curve(AUC)=81.85±14.24mghL-1; 2)s.c. administration: T1/2ka= 1.36± 0.75 h,T1/2β=17.92 ± 9.19 h,Tmax=3.18±1.05h,Cmax=5.12±0.99μgmL-1,AUC=56.73±5.25mghL-1,F=71.03 ± 14.15%. The results indicated that clorsulon in sheep following a single s.c.administration was absorbed rapidly and eliminated slower than that following a single i.v.administration,and showed a better bioavailability.