Guillingji powder, a complex prescription of traditional Chinese medicines, has been pharmacologically shown to be a possible anti-aging agent, and also used for the treatment of male hypogonadism and female dysgenesis. Since the levels of numerous brain monoamines and their metabolites such as norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) have been correlated with aging, we examined the effects of Guilingji powder and its extract on such monoamines and metabolites in the cerebrum and the cerebellum of mice using HPLC-ECD. The results showed that dietary intake of Guilingji powder had the effect of increasing the NE level and the DOPAC/DA ratio, and decreasing the 5-HT level and 5-HT/NE ratio in the cerebrum. In the cerebellum, the powder did not produce any changes in the levels of the compounds investigated. The extract of Guilingji, on the other hand, not only increased the NE level and the DOPAC/DA ratio but also the 5-HIAA/5-HT ratio in the cerebrum. However, the extract did not decrease the 5-HT in the cerebrum, although it decreased the 5-HT/NE. Unlike the powder, the extract had an effect in the cerebellum, which increased the DOPAC/DA ratio. These results suggest that Guilingji may have the action of modulating the levels and the metabolism of monoamines.