Objective:To examine incorporation of Western medicine into vegetable drugs (traditional Chinese medicine) by using UV absorption spectrum. Method: Nine chemicals were respectively mixed into Siwu decoction(made from Prepared Rehmannia Root

White Peony Alba

Chinese Angelica Root and Chuanxiong Rhizome). Using weighted correlation analysis (based on the correlation

with larger weighted value around peaks and valleys of UV absorption spectrum) to analyze the variation on spectrum between before and after the mixing. Result: Six chemicals influenced UV absorption spectrum significantly after they were respectively mixed into Siwu decoction

the similarity between before and after mixing was low with Spearman'sρ<0.94

but the other 3 chemicals was not

with Spearman'sρ>0.95. Conclusion: UV absorption spectra can be used for identifying the chemicals mixed illegally into decoction of traditional Chinese medicine.