Object : This study was designed to assess the protective effects of Jowiseungchungtang on cognitive decline of the patients with early DAT[Dementia of Alzheimer Type]. Method : 15 patients with early DAT and 10 healthy elderly subjects were measured by using auditory ERP and K-DRS, and after 9 months again. During 9 months the patients with early DAT were administered with Jowiseungchungtang. Result : 1. The score of K-DRS increased in two group but it was not significant. 2. The latency of ERP P300 component increased in 2nd test of the normal group, but did not increase in 2nd test of patients group. 3. The amplitude of ERP P300 component showed the significant difference in electrode location in patients group, but it did not show any typical property. Conclusion : The results suggest that Jowiseungchungtang may have protective effects on cognitive decline in the patients with early DAT.