Abstract: Six compounds have been isolated from the root of Paeonia suffruticosa and P. lactiflora. They were identified as paeoniflorin (Ⅰ), benzoylpaeoniflorin (Ⅱ), oxypaeoniflorin (Ⅲ), paeonol (Ⅳ), paeonoside (Ⅴ) and paeonolide(Ⅵ) Based on the findings that compounds Ⅰ～Ⅵ are the main active constituents in Paeoniaceae, the contents of these constituents in the root of 23 Paeonia taxa including 19 different species and 6 varieties were determined by means of a quantitative HPTLC scanning method. The result showed that paeoniflorin occurred ubiquitously as the major and characteristic constituent in all the species examined; P. lactiflora and P. tenuifolia contained the highest amount of paeoniflorin and hence,worthy of further consideration for their resource utilization; Paeonol and paeonoside were found to be restricted to the woody Sect. Moutan (the main source of 'Mu-dan-pi') are notably absent in the herbaceous Sect. Paeonia (the main source of 'Shao-you'). This differentiation may be used as a chemical criterion for quality control of 'Mu-danpi' and 'Shao-yao'. All these data may also contribute to the understanding of the chemosystematics and phylogeny of the family Paeoniaceae.