Abstract: The Aristolochia species is an important genus of Aristolochiaceae among the Chinese drugs such as Aristolochia debilis; A. manchuriensis; A. Kaempferi; A. mollissima etc. From these, the Chinese drug Ching-Mu-Hsiang, root of A. debilis, S. et Z. was reported to be effective n hypertension therapy. Therefore, we schemed to investigate about 40 kinds of this species which can be collected in this country. In the present article, the authors report the isolation of five constituents isolated from the root of A. debilis. The constituent(Ⅰ) is C₁₇H₁₁O₇N, yellow needles, m.p. 275° and its methylester C₁₈H₁₃O₇N, m.p. 265°was prepared. The melting points closely resemble those of isoaristolochic acid rather than aristolochic acid, which melts at 281--6°, and whose methyl ester melts at 281°. The authors have successfully isolated a new nitrogen-contained acid under the repeated and careful check by paper chromatography. It is C₁₈H₁₃O₇N, yellow needles, m.p.350°which is provisionally named Debilic acid (Ⅱ). It appears in many respects similar to (Ⅰ), both in physical and chemical properties, but it can clearly be distinguished from each other by paper chromatography when using the solvent system of alcohol/ammonia/ aq. (80:5:15) from which (Ⅰ) shows a spot at R_A=1.00 and (Ⅱ) at R_A=0.87. Owing to their similarity in character and the difficulty in separation, one can easily realize now why the previous workers encountered so many discrepencies that should be occurred. It appeared that on admixture of (Ⅰ) & (Ⅱ), a series of "homogeneous" crystalline compounds can be obtained and the m.p. varies from 260°to over 300°. The constituent of (Ⅲ) is a kind of colorless needles, m.p. 256--6°. The analytical results show the formula as being C₄H₆0₃N₄. It was identified as allantoin, and no melting point depression has been observed on admixture with its authentic sample, and a specific mercury compound could be prepared on addition of Hg(NO₃)₂. Lastly, a tertially base (Ⅳ), m.p. 145°and another quaternary base (Ⅴ) were isolated from the aqueous mother liquid. (Ⅴ) formed several kinds of crystalline salts, namely; picrate (m.p. 218°), picrolonate (m.p. 281°), reineckate (m.p. 256°) and an imputed chloroplatinate. However, due to poor yields of (Ⅳ) and (Ⅴ), it was unable to carry out the analysis.