The experiment was conducted to study the effects of glutamine (Gln) on antioxidant function of broilers under heat stress. Two hundred and forty 1 day-old Kebao-500 broilers were randomly selected and divided into 6 groups with 4 replicates, and 10 chicks in each replicate. Six groups were consisted of group Ⅰ (control group) to Ⅵ, which was supplemented with Gln at the level of 0, 0.4%, 0.8%, 1.2%, 1.6% and 2.0% in 6 basal diets, respectively. The experiment lasted for 28 days (from 15-day-old to 42-day-old) During the experimental period, the temperature maintained at (35±2) ℃ for 8 h from 09:00 to 17:00 and maintained at (30±2) ℃ from 17:00 to 09:00 of the next day. The relative humidity of the chicken house was controlled from 70% to 80%. The effects of Gln on the activities of GSH-Px, SOD and CAT, the ability of inhibiting hydroxyl radical (·OH) and resisting superoxide anion free radical (O-2·), and the content of MDA, T-AOC in serum and intestine of broilers under heat stress were studied. The results showed that, at 28 days of age, supplemental Gln could significantly enhance the activities of GSH-Px, SOD and T-AOC (P<0.05), raise the ability of inhibiting ·OH (P<0.05), reduce the content of MDA in serum and intestine (P<0.05), and increase the activity of CAT in serum (P<0.01). At 42 days of age, supplemental Gln could significantly increase the activity of CAT and T-AOC in serum and intestine (P<0.05), and reduce the content of MDA in serum (P<0.05). The results indicate that Gln supplementation can improve the antioxidant function in serum and intestine of broilers under heat stress, and the supplemental effects of earlier period are better than that of the later period. In conclusion, the suitable supplemental level of Gln in diet is recommended as 1.6%.［Chinese Journal of Animal Nutrition，2011，23（4）：695-702］