This study was conducted to investigate the effect of increasing dietary levels of chromium, vitamin C and their combination on the productive performance and immune response of laying hens under summer season of Egypt (31.5°C). One hundred and twenty Hy-line hens were evenly distributed to four groups of 30 hens each. The first group (control) was fed a basal diet without any supplementation. The second group was fed the basal diet containing 80 mg Cr/kg and third group was fed 205 mg vitamin C/ kg diet. Finally, the fourth group was fed a basal diet containing 80 mg Cr/kg and 250 mg vitamin C/kg. When the chicks were 36 weeks of age, a delayed-type hypersensitivity test was performed. Also, blood samples were collected at 40 weeks of age for the determination of plasma calcium, plasma phosphorus and plasma cholesterol. It could be noticed that the chromium, vitamin C and their combination had no effect on body weight. The laying hens fed a basal diet containing 80 mg chromium significantly consumed less feed compared to control group. Opposite trend was noticed in the other fed diet containing 250 mg vitamin C. The higher levels of chromium, vitamin C and their combination significantly increased shell thickness, plasma calcium and plasma phosphorus compared to control fed-group. Conversely, the plasma cholesterol and egg yolk cholesterol were significantly reduced when laying hens fed a diet added higher level of chromium, compared to the control-fed group. Cell-mediated immune function, as measured by an in viva hypersensitivity response to an intradermally injection of a T lymphocyte-dependent mitogen (phytohemagglutinin-P), as significantly increased in the laying hens fed a diet containing chromium, vitamin C and their combination compared to the control groups. Finally, it could be noticed that the chromium and ascorbic acid supplementation at higher levels is beneficial for laying hens during heat stress to improve the performance and immunity.