The current study aimed to investigate the effect of garlic juice supplementation with broiler drinking water on performance, immune response, lipid profile, blood picture and activity of liver enzymes under heat stress. For this purpose 100 four days aged broiler checks (Ross) were allocated into control (C) and three treatment groups (25 each). All group checks were housed at 5 ºC above normal ambient temperature during the experiment. Treatment groups (T1, T2 and T3) checks were supplemented with 0.5, 1 and 1.5 ml/L, respectively, with garlic juice in drinking water (6 hrs a day). Food and water were supplemented ad libitum. Body weights were monitored every five days and blood samples were obtained at 25 days for assessment of blood picture and antibody titers after vaccination, total cholesterol and triglycerides concentrations and activity levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were estimated. At 30 days age, T3 group broiler checks reported higher body weights than other groups. Total number of white and red blood cells, hemoglobin concentration, hematocrit levels and ratio of heterocytes to lymphocytes increased significantly in treated groups, whereas significant decline of cholesterol and triglycerides concentrations as well as ALT and AST levels were shown in T3 group broiler checks. Significant increase was shown in the levels of antibody titers against both Newcastle (ND) and infectious bursal disease (IBD) vaccines. In conclusion, treatment of broiler checks early with garlic juice increase broiler performance and immune response against vaccination program and may be protect the broilers from heat stress.