Abstract: This experiment was conducted to study Pharmacokinetics of ivermectin in Oncorhynchus mykiss following a single oral administration or intraperitoneal injection. Pharmacokinetics of ivermectin in Oncorhynchus mykiss was studied following a single oral or intraperitoneal injection at dose of 0.3 mg/kg by high-performance liquid chromatography-ultraviolet detection(HPLC-UV). The results showed that: after oral administration, the concentrations versus time of ivermectin in plasma and muscle were well described by two-department open model with first-order absorption, while those in liver and kidney were well described by one-department open model with first-order absorption; after intraperitoneal injection , the concentrations versus time of ivermectin in plasma, muscle, liver and kidney were well described by one-department open model with first-order absorption. After oral administration, the pharmacokinetic parameters in plasma were as follows: AUC=123.709 mg/(L?h), Ka=3.749 h^-1, t_1?2ke=466.569 h, T_max=0.454 h, C_max=0.319 mg/L; After intraperitoneal injection, the pharmacokinetic parameters in plasma were as follows: AUC=52.560 mg/(L?h), Ka=5.033 h^-1, t_1?2ke=103.236 h, T_max=1.317 h, C_max=0.350 mg/L. It stated that pharmacokinetics of ivermectin in Oncorhynchus mykiss were differences between two different administration routes, and intraperitoneal injection led to more rapid absorption and elimination than oral administration.