Abstract: To study the metabolic law of Ciprofloxacinum in Chinese mitten-handed Crab,Eriocheir sinensis,its concentrations both in hemolymph and muscle were measured by using RP-HPLC after intramuscular injection at a dose of 8.17±0.56mg·kg-1and 6.25±0.85mg·kg-1 to male and female crab at the first experiment,or at a dose of 5.99±0.27mg·kg-1 and 6 05±0 32mg·kg-1at the second experiment respectively The concentration of Ciprofloxacinum in the hemolymph was the highest immediately after injection Within an hour,the blood-drug concentration dropped sharply On the other hand,the concentration in the muscle reached maximum an hour after injection and decreased gradually thereafter It was lower than 1μg·mL-1(g-1)at 120h and undetectable at 216h This finding indicated that the injected Ciprofloxacinum moved into muscles via hemolymph in the crab.The concentrations of Ciprofloxacinum in hemolymph were best described by a two-compartment open model with first-order absorption To male and female crab,the pharmacokinetic parameter,T 1/2β,was 40.34±1.48h and 22.07±0.31h respectively Also,Pharmacokinetic difference between male and female crab was observed.