Abstract: Total isoflavones extracted from red clover were supplemented in the diets (4.38 mg/kg feed) of male Redbro broilers (45-56 days of age,n=15).Body weight gain of treated male chickens increased by 5.1%,feed conversion increased by 9.2%.Slaughter results showed that abdominal fat pad and ratio of abdominal fat pat to carcass weight decreased significantly,whereas comb weight,testis weight increased.The analysis of correlation coefficient between comb.testis and body weight,the observation of paraffin sections of testis and the radioimmunoassay (RIA) of the serum testosterone levels indicated that the total isoflavons could elevate serum testosterone levels and promote the development of the reproductive organs of male broiler chickens.