In this study, we analyzed and quantified the amounts of bioactive phenolic constituents, xanthotoxin (1), oxypeucedanin (2), and imperatorin (3) in each part of the root of Angelica dahurica by HPLC, which validated by ICH guide lines comparing the linearity, intra day precision, inter-day precision. As a result, the amount of imperatorin 2.96% in the rootlet was two fold higher than that of the main root 1.32%. On the other hand, the amounts of xanthotoxin and oxypeucedanin in the rootlet showed similar to those of main root. In addition, the cortex of root is more plentiful of three consitituents (0.66%,0.53%, and 1.85%) than those of xylem (0.29%, 0.05%, and 0.07%). These results show that the rootlet and cortex contain a large amount of bioactive phenolic constituent including xanthotoxin, oxypeucedanin, and imperatorin than other parts of the root.