An experiment was conducted to evaluate the effect of tamarind seed coat extract on the average daily weight gain, feed intake and feed conversion rate of broilers. Broilers were divided into 6 groups and received polyphenols from tamarind seed extract at 0 (control), 100, 200, 300, 400 and 500 mg/kg in their diets for 21 days. The results revealed the following information: During the period of 36-42 days of age, the average daily weight gain of broilers that received tamarind seed coat extract at 100 mg/kg in their diet was significantly higher than the weight gain of broilers that received tamarind seed coat extract at 0, 200, 400 and 500 mg/kg in their diets (p<0.05). Throughout the experimental period, the average daily weight gain tended to be highest in the group that received tamarind seed coat extract at 100 mg/kg in their diet. The feed intake and feed conversion rate of broilers in all groups were not significantly different (p>0.05). This study demonstrated that tamarind seed coat extract has a property similar to antibiotic feed additives and provides slightly improved average daily weight gain