Abstract: The pharmacokinetics of norfloxacin were analyzed in whiteleg shrimp (Penaeus vannamei) following intramuscle in- jection and oral administration1 The curvilinear trend of the hemolymph concentration versus time data were almost similar follow-ing intramuscle injection at salinities of 1 and 15. The hemolymph concentration versus time at the salinities of 1 ppt and 15 ppt were well described by a two-department model, and the pharmacokinetic models were C0= 35.422 × e-9.778t+ 41363 × e-0.165t at salinity of 1 and C0= 351144 × e-13.335t+ 7.888 × e-0.608tat salinity of 15. There were significant differences in some phar2 macokinetic parameters of norfloxacin in P1 vannamei between at salinities of 1 and 15. The distribution half-life(t1/ 2 α),disposi-tion half-life(t1/ 2 β),area under curve (AUC), total body clearance (CLs) and apparent volume of distribution (Vd)following in2 tramuscle injection at salinity of 1 were 0.071h,4.208h,30.06 μ g· h/ mL, 332.7 mL/ kg· h and 2016 mL/ kg, respectively1 The corresponding values at salinity of 15 were 0.052h, 1.140h, 15.61 μ g· h/ mL, 640.6 mL/ kg· h and 1054mL/ kg, respectively1 Following oral administration at dose of 30 mg/ kg,the hemolymph concentration2time profile of norfloxacin in whiteleg shrimp ex-hibited two peaks of hemolymph norfloxacin concentration, which occurred at 4h and 12h,and the hemolymph norfloxacin peak concentrations were 2.86 μ g/ mL and 2.04 μ g/ mL, respectively1 The area under curve and total body clearance followingoral ad-ministration were 43.50 μ g· h/ mL and 689.7 mL/ kg· h1 The hemolymph concentration-time profile of norfloxacin following oral administration at dose of 15mg/ kg also exhibited two peaks, which was similar to that at dose of 30mg/ kg.But the second Cmax at dose of 15mg/ kg occurred at 8h. There were no marked proportion between the dosage of norfloxacin and the hemolymph nor-floxacin concentration1