This study aimed to inspect the effects of consuming two different doses of the brown seaweeds "Sargassum latifolium" by heat stressed growing Barki ram lambs for 60 days on their growth performance, physiological and behavioral responses. Twenty Barki ram lambs 6–8 months old with average of 29.26 ± 2.09 kg live body weight were divided into four equal experimental groups. Lambs in the first group were kept in comfortable environmental conditions and were not offered seaweed and assigned as control (C). Animals in the second group were exposed to heat stress and were offered the diet without seaweed (T0). Animals in the third (T1) and fourth (T2) groups were exposed to heat stress and were supplemented with 2 and 4% (from CFM) brown seaweeds, respectively. Feed intake and body weight were recorded daily. Complete blood count and plasma biochemical parameters were assessed biweekly while behavioral responses were measured in the last week of the experiment. Animal had brown seaweeds in T1 and T2 groups increased (P<0.01) average daily gain and total body weight gain as compared to their counterparts exposed to heat stress (T0). Moreover, lambs of T2 achieved the best feed conversion ratio (8.37). Seaweed supplementations increased (P<0.05) leukocyte, hematocrit and hemoglobin concentration. Feeding lambs with a diet containing 4% brown seaweeds increased (P<0.01) serum total protein, albumin, potassium level, but decreased (P<0.01) serum total lipids, triglycerides, total cholesterol as compared with control ones. Supplementation with brown seaweeds affected significantly daily water intake and some behavioral parameters. It can be concluded that supplementation with brown seaweed (2% and 4% from CFM) to heat stressed Barki ram lamb in summer improved productive performance through improving growth rate, blood constituents, beside ingestive, standing and lying behavior.