To investigate the effects of flavomycion on the immunity organs of mice,the mices were randomly divided into three groups: fed with normal diet(control group),the diets supplemented with 20 mg/kg(experimental group A) or 80 mg/kg(experimental group B) respectively for 30 d.After 30 days,the indexes of thymus and spleen were calculated,at the same time,the structure of thymus and spleen were observed.There was no significant difference in thymus or spleen between control group and experimental groups.The result suggested that flavomycion could not affect the immunity organs of mice.