The aim of this experiment was to determine the effect of polyphenols extracted from tamarind (Tamarindus indica L.) seed coat on physiological changes, oxidative stress and production of male broilers maintained at high environmental temperatures. The results found that body temperature and respiratory rate of broilers maintained at 38 +/- 2 degrees C was higher than broilers maintained at 26 +/- 2 degrees C (P < 0.05). On day 1, the heterophil/ lymphocyte ratio of broilers maintained at 38 +/- 2 degrees C and received polyphenols at 300 and 400 mg/kg in diets was lower than broilers that received polyphenols at 0 and 200 mg/kg in diets (P < 0.05). At week 1, the malondialdehyde of the broilers maintained at 38 +/- 2 degrees C who received polyphenols at 400 mg/ kg in their diet was lower than broilers that received polyphenols at 100 and 200 mg/kg in diets (P < 0.05). At week 1, the body weights of broilers that were maintained at 38 +/- 2 degrees C who received polyphenols at 100-500 mg/ kg in diets, and broilers maintained at 26 +/- 2 degrees C were higher than that of the control group which had not been treated with a polyphenol diet (P < 0.05). This study indicated that polyphenols could reduce heat stress, oxidative stress and improve the growth rate of heat-stressed broilers.