The high ambient temperature during summer causes various negative effects compromising laying hen performance. The present study aimed at studying the possible effects of yeast culture and/or vitamin C dietary supplementations to laying hens on alleviating the negative effects imposed by high ambient temperature during summer. A total of 200 Hy-Line Brown hens 32 weeks old, were randomly allocated to four groups with 50 hens divided at five replicate each. The first group received basal diet without any supplementation and served as control group (C). The groups 2, 3, and 4 received basal diet supplemented with 0.2% dried yeast (Yeast), 250 mg of vitamin C (Vit-C ), and 0.1 % dried yeast + 125 mg vitamin C (Yeast+Vit-C) respectively. Hens were raised in wired cages in an open house. The experiment was carried out during summer, and the averages ambient temperature and relative humidity were 30.9±1.3 ͦC and 48.8±0.1%, respectively. Feed intake, feed conversion, egg production were recorded and egg quality parameters were measured. Yolk cholesterol, total lipid and plasma biochemical contents were determined. Antibody titer of Newcastle (NDV), Infectious Bronchitis (IBDV) and Avian Influenza (AIDV) disease virus were quantified after 30 days of immunization. Ileum Salmonella, E-coli and total bacterial count (TBC) were also quantified. Yeast supplementation with or without vitamin C showed a positive effect on feed intake, feed conversion, egg production and egg quality. Improvement in both external and internal egg quality parameters were observed for dietary supplemented groups compared to the control group. Yolk cholesterol and total lipid decreased significantly with all supplementations. The antibody titer for the immunized viral diseases NDV, IBDV and AIDV significantly increased with yeast supplementation. Ileum E-coli and TBC were significantly decreased by yeast supplementation. It can be concluded that yeast culture is a powerful dietary supplement during hot season, since they can alleviate the negative effects of heat stress on laying hen performance and egg quality. Also, they can be used as an immunomodulation of pathogen challenged animals or pre-immunization. Moreover, vitamin C can also be used as anti-stress but with less pronounce positive effect.