This study was conducted to investigate the effect of probiotic (PROBAC plus®) supplementation on growth performance, carcass characteristics, and clinical health parameters of broilers reared under high temperature (32-35oc) from age of 22 to 42 day. A total of 120 broiler chicks were divided into 4 groups at age of one day. The first group was control (fed with basal diet), second was broilers reared at high temperature (fed with basal diet), third was broilers reared at high temperature (fed basal diet + probiotic) and fourth was probiotic group (control + probiotic). Growth performance was determined weekly. At day 42, 10 birds from each group were randomly selected and slaughtered to determine the carcass characteristics and to collect blood samples. Serum blood biochemicals and thyroid hormones were estimated. The obtained results showed that heat stress have reduced the performance, carcass traits and showed alterations in clinical biochemical parameters. Addition of probiotic to diets of birds reared with or without stress enhanced growth performance, carcass traits and improved clinical blood parameters. The results suggest that probiotic can be used to counteract the adverse effects of heat stress in addition to its efficacy as growth promoter.