MeOH extracts of eight herbal medicines were investigated for the effects on catecholamine biosynthesis and tyrosine hydroxylase (TH) activity in PC12 cells. Among them, the MeOH extracts of Polygalae Radix and Rehmaniae Radix showed 32 and 22% inhibition on the dopamine biosynthesis, respectively at a concentration of $40{mu}g/ml$ medium. But, the TH activity was reduced by the treatment of Polygalae Radix. These results suggest that Polygalae Radix has an inhibitory effect on the catecholamine biosynthesis by the reduction of TH activity in PC12 cells.