Abstract: ObjectiveThe study aimed to evaluate the chronic toxicity of enramycin on rats and provide scientific ba-sis for its rational use.MethodA total of 240 SPF-grade Wistar rats were selected to test the chronic toxicity of enramy-cin. High-dose group(1000 mg/kg),medium-dose group(200 mg/kg),low-dose group(10 mg/kg)and blank control group were divided according to enramycin half lethal dose(LD50). Enramycin was added to rat feedstuff in high,medium and low doses to be processed into customized feedstuff. The rats were fed once a day,continuously fed for six months. Then,the chronic toxicity of enramycin in rats was evaluated through clinical observations,hematology analysis,blood serum biochemical examination,organ coefficient and pathological examination.ResultDuring the entire test period(six months),rats in every treatment group were normal in drinking and urination,and were in good spirits with glossy coat, no rat was dead. Compared with the control group,there was no significant change in the body weight of each enramycin dose group(P>0.05,the same below). With the increase of drug dosage and prolongation of administration time,enramycinonly had certain effects on the number of neutrophils in rats,and it slightly affected blood serum indexes of alkaline phos-phatase,aspartate aminotransferase and albumin. In terms of organ coefficient,only six months after continuous medica-tion,the organ coefficients of liver and spleen only in high-dose group rats was significantly lower than that of the control group(P<0.05),and there was no significant change in other organ coefficients. With the increase of drug dose and pro-longation of administration time,enramycin slightly affected the liver,lung,kidney and heart of rats. The main manifes-tations were:in high-dose group,the cells around its central vein of liver tissue were slightly swollen;lung tissue had cer-tain degree of congestion,and the interstitial space was slightly widened;renal tissue was slightly congested,and renal tubular epithelial cells were slightly swollen;myocardial fibers were slightly atrophied,and myocardial interstitials were widened.ConclutionEnramycin has very low toxicity. With increase of drug dosage and prolongation of medication time,its chronic toxicity effects on rat is very slight,that is,the safety of enramycin in clinical medication is very high.