Objectives: Anti-oxidants are known to prevent neuronal diseases with pathological and physiological changes such as the brain atrophy and cognitive impairment. This study was designed to investigate the protective effects of Korean ginseng on the oxidative stress induced pathologic changes, and develop new animal model for the brain atrophy. Korean ginseng has anti-oxidant, anti-aging, and protective effects on the brain ischemia. Methods : The intracerebroventricular (ICV) hydrogen peroxide ($H_2O_2$) injection into mice was conducted to generate oxidative stress. Results : The ICV $H_2O_2$ (1 M, $5;{mu}l$ injection did not induce either convulsion or death in the acute phase. At the end of second week, cognitive impairment and pathologic change of the brain were observed. The massive brain atrophy was found in the $H_2O_2-injected$ mice, especially in the hippocampus and thalamus. Treatment with Korean ginseng showed a protective effect against the brain atrophy. The $H_2O_2$ injected mice revealed cognitive impairment in the passive avoidance test, and Korean ginseng alleviated cognitive impairment. Conclusion : The results indicate that Korean ginseng has a protective effect on the oxidative stress-induced neuronal damages.