This study was conducted to determine the possible use of Red Ginseng marc as stress inhibiter in thermal stress (temperature humidity index 86) and lipopolysaccharide (LPS) - exposed laying hens by investigating their effects on laying performance, blood biochemical parameters, immunoglobulin concentration and serum superoxide dismutase (SOD) like ability. A total of forty-five 52-wk-old laying hens (ISA Brown) were divided into 3 treatment groups with 5 replicates of 3 birds in each group. NC (negative control, no immune substances), PC (positive control, β-glucan 25 ppm) and RGM (Red Ginseng Marc 3%) were added in feed with respective substance. Egg production in RGM was significantly increased in comparison with NC groups for 8 weeks (P<0.05). On blood biochemical parameters, effects of ambient temperature is definite by showing significant difference in aspartate aminotransferase and others (P<0.05), but RGM both before and after thermal stimulation have no significant difference in comparison with other groups. And for 3 weeks after thermal stimulation, laying performance was also not significantly different among treatments. Immunoglobulin M content and SOD like activities after challenge with LPS were higher in the RGM and PC than NC (P<0.05). In conclusion, although ineffective as inhibiter in thermal stress, dietary supplementation of Red Ginseng marc improved SOD like activity and immune system by regulating immunoglobulin content in laying hens. These findings have laid the foundation for future studies of immunomodulation in laying hens fed Red Ginseng Marc and of evaluation of heat stress inhibitor.