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The compound ent-7β-hydroxy-15-oxo kaur-16-en-18-yl acetat (CT1) is the major constituent and found uniquely in the medicinal plant Croton tonkinensis Gagnep. This compound was also found to have numerous pharmaceutical activities, therefore, it should be considered as a main bioactive constituent of this plant material. However, the Vietnamese Pharmacopoeia IV (2009) postulates the qualitative analysis of this herb by thin layer chromatography (TLC) using standard sample of herbal Crotonis tonkinensis. In this study, we indicate that the material of this herb could be qualitative analysis by TLC and HPLC by using CT1 as a reference compound. The study also develops a method for quantitative analysis of the compound CT1 in the medicinal materials Crotonis tonkinensis by HPLC (column C18; UV detector at 233 nm; solvent acetonitril-water 65:35). The contents of CT1 in some herbal samples collected in northern Vietnam were determined to be 0,507–1,274% in leaves, 0,318–0,461% in green stems and 0,135–0,176% in old stems, indicating that leaves contain highest amount of CT1. The results of this study suggest that the compound CT1 should be used as a reference compound for qualitative and quantitative analysis of the material herb Crotonis tonkinensis in Vietnamese Pharmacopoeia.