In this study, we investigated the effects of Ginseng Radix (G), Rehmanniae Radix (R), and Fermented red-ginseng extracts (FRG) on cognitive function in scopolamine-induced memory-impaired mice. We measured the effects of G, R, and FRG on the improvement of memory and cognition via behavior analysis. In addition, we measured the acetylcholinesterase (AChE) activity in the hippocampus of each group of mice. The expression of β-amyloid, Tau, and BDNF in the brain tissues were observed through immunohistochemical staining. Ginseng Radix (G) and Fermented red-ginseng (FRG) have effectively improved cognitive function in the water maze test. Ginseng Radix (G), Rehmanniae Radix (R), and Fermented red-ginseng (FRG) have improved the willingness of mice to explore the new environment, as confirmed by Y maze test. In addition, immunohistochemical staining revealed that Ginseng Radix (G) decreased the expression of β-amyloid and Tau in the hippocampus. In addition, fermented red-ginseng (FRG) increased the expression of BDNF. Ginseng Radix (G), Rehmanniae Radix (R), and Fermented red-ginseng (FRG) have decreased the concentration of acetylcholinesterase in the hippocampus as compared with the control group of mice. In conclusion, Ginseng Radix (G), Rehmanniae Radix (R), and Fermented red-ginseng (FRG) are considered to have the potential for development as candidate drugs to control the progression of Alzheimer's disease (AD).