Yukmijihwang-tang (YMJ), also known as Luweidihuang-tang in China, has been widely used as a general herbal tonic for hundreds of years in many Asian countries. This study examines whether YMJ derivatives (YMJd) enhance cognitive ability in normal human subjects and discusses its potential as treatment for dementia patients with deficient cognitive ability. Subjects were divided into two groups, the placebo-treated group (n = 15) and the YMJd-treated group (n = 20). K-WAIS tests, a Korean version of an individual intelligence quotient (IQ) test, and a P300 latency assessment of event-related potential (ERP) were conducted in order to measure changes in cognitive ability before and after 6 weeks of YMJd treatment. The K-WAIS mean scores of the group treated with YMJd were significantly higher than those of the placebo group (p < 0.05), and their mean P300 latency was substantially shorter (p < 0.005). These results suggest that YMJd treatment accelerates the speed of information processing and enhances cognitive ability. YMJd treatment may help dementia patients or the elderly recover from cognition deficiencies or degeneration in clinic.