The study was performed to evaluate the effect of vitamin C and/or folic acid on performance, some blood constituents, oxidative stress marker (malondialdehyde (MDA), some physiological measurement (body temperature, respiration rate and blood (pH) and immune response to sheep red blood cells (SRBC's) of Al-Salam laying hens under hot environmental temperature of summer month's conditions in Egypt. A total number of one hundred and twenty, 30^th weeks old Al-Salam hens were randomly selected and distributed into four equal groups, 30 birds each, in three replicates, 10 birds each. Birds in the 1^st group were served as control, while those in the 2^nd group were fed on a diet with vitamin C (250 mg/kg diet). The 3^rd group was received a diet supplemented with folic acid (1 mg/kg diet) whereas, the 4^th group was given a diet inclusive vitamin C plus folic acid. All groups were put under observation for 16 weeks. Supplementing heat-stressed laying hens with vitamin C and folic acid improved performance compared to the control group. Digestibility of dry matter, organic matter, crude protein and ether extract were highest in the vitamin C and/or folic acid groups and lowest in the control group (P < 0.05). Retention of Ca, P, Zn and Cu were highest in the vit. C + folic acid group and lowest in the control group (P < 0.05). Furthermore, serum malondialdehyde (MDA), cholesterol and glucose concentrations decreased, whereas, serum total protein, albumin, globulin, calcium and phosphorus concentrations increased with dietary vitamin C and folic acid supplementation (P < 0.05) compared with the control group. However, the combination of vitamin C and folic aid provided greatest results. Body temperature, respiration rate and blood pH were lower in the vit. C + folic acid group and higher in the control group. The results showed that heat exposure reduced antibody titer against sheep red blood cells (SRBC's). However, vitamin C and/or folic acid supplementation enhanced humoral antibody response against SRBC's. The results of the study indicate that, separately or in combination, vitamin C and folic acid supplementation attenuates the decline in performance and antioxidant status caused by heat stress. Such supplementation may offer protection against heat stress-related depression in performance of local laying hens.