Abstract: In the tank with a constant water temperature of 25±1℃, American eels were administered with mequindox (MEQ) for the study. The eels were either orally fed with a feed at a single MEQ dosage rate of 120 mg/kg, or placed in a water bath containing 5 mg MEQ/L for 18 h. Samples were collected periodically to obtain MEQ concentrations in the blood plasma, muscle, liver, and kidney of the eels by HPLC, while MEQ pharmacokinetics analyzed. The pharmacokinetic characteristics of MEQ were found to be fast absorbed, evenly distributed, rapidly eliminated, and left with low residues in the fish. Under the oral administration, the pharmacokinetics of the blood plasma showed a T_max at 0.75 h, C_max at 4 115 μg·L^-1, T_1/2 at 7.40 h, and CL/F at 41.89 L·kg^-1·h^-1. The concentrations of MEQ in the organs were below the detectable level after 72 h. For the medicated bath treatment, the pharmacokinetics of the eel blood plasma indicated T_max to be 0.25 h, C_max 435.6 μg·L^-1, T_1/2 0.26 h, and CL/F 1.241 L·kg^-1·h^-1. The MEQ in the organs became not detectable after 2.5 h. The distribution of plasma MEQ in the eels under either treatment fitted the one-compartment open model.