Pharmacokinetics of ivermectin in Carassius auratus was studied following a single oral or intramuscular administration at dose of 0.4 mg/kg.After following these two different administration routes,IVM concentration-time cruves in most tissues of C. auratus exhibited multi-peak phenomenon.After intramuscular administration,noncompartmental pharmacokinetic parameters were as follows:C_max=0.445 mg/L, T_max=48 h,t_1/2z=524.2 h, MRT_{(0-∞ )}=788 h and AUC_{(0-∞ )}=289.2(mg/L)·h.After oral administration,non-compartmental pharmacokinetic parameters were as follows:C_max=0.264 mg/L, T_max=8 h, t_1/2z=153.9 h,MRT_{(0-∞ )}=269.78 h,and AUC_{(0-∞ )}=83.77(mg/L)·h.Comparing parameters of these two administration routes,we found that the rate of absorption and elimination following the oral administration was relatively higher than that following the intramuscular administration,while the bioavailability of the latter was higher.The AUC_0-600 values in different tissues of C.auratus have same sequence:gonad>blood>kidney>hepatopancreas>muscle.IVM shows some kind of accumulative effect in both gonad and kidney,as high IVM concentration and slow elimination rate and long MRT in these two tissues,especially in ovary.When water temperature is 25 ℃,we suggest IVM withdrawal period in C.auratus no less than 25 or 15 days following a single intramuscular or oral administration respectively at dose of 0.4 mg/kg.As drug withdrawal period had significant relationship with both water temperature and administration dose,so drug withdrawal period should be adjusted properly according to the practical aquaculture conditions.