Abstract. Due to negative effects of high ambient temperature, the present study was conducted to investigate the effects of Portulaca oleracea hydroextract (PHE) and zinc (Zn) on the growth performance and immunity of broiler chickens reared under high summer ambient temperature conditions. A total of 420 day-old male broiler chickens (Ross 308) were randomly allocated to seven dietary treatments each replicated four times with 15 birds per replicate. The basal diet as the control diet was supplemented with 100 mg kg −1 butylated hydroxytoluene (BHT), or 300 and 600 mg kg −1 of PHE, 100 mg kg −1 of zinc and 100 mg kg −1 of zinc plus 300 or 600 mg kg −1 of PHE (ZP300 and ZP600). The result of the present study showed that Zn, PHE and their combination did not alter daily feed intake and feed conversion ratio. Although there was a tendency toward an increase in broiler body weight at 24 and 44 days of age (P = 0.059 and P = 0.061), the body weight of birds fed the basal diet supplemented with Zn reduced at day 10. The birds fed diets supplemented with BHT or ZP600 showed lower aspartate aminotransferase (ASAT) and lactate dehydrogenase activity at 24 days of age (P < 0.05), but it remains lower in the ZP600 group only for ASAT activity level at day 44. The results of the present study suggest that dietary PHE and Zn supplementation partially improved body weight and serum antioxidant capacity, superoxide dismutase activity and antibody titer against sheep red blood cells and Newcastle diseases in the broiler chickens during summer conditions.