Abstract: To evaluate the effect of vitamin C and zinc on performance and immune-competence during heat stress. Four hundred and eighty, 1 day old Arbor Acres broiler males and females were used and raised in either a thermoneutral (control) or heat stressed (40°C) environment where different levels of vitamin C and zinc were supplemented. Humoral immunity was assessed by intravenous injection of Sheep Red Blood Cells (SRBC) followed by evaluation of serum for antibody titers in primary and secondary responses. Heat stressed birds that supplemented with vitamin C and Zinc showed greater (p = 0.5) body weight, higher daily gain, better feed conversion ratio and less mortality than the non-supplemented control group. Total, IgM and IgG antibody titers for primary and secondary responses were significantly increased in birds receiving vitamin C and zinc with variable levels according to the concentration of vitamin C and zinc. These results indicated that the immune response of broilers can be influenced under heat stress conditions by combination of different levels of vitamin C and Zinc in the diet. The recommended levels of vitamin C and Zinc depend on environmental conditions and other factors which still need further manipulation.