Abstract: In order to establish the quantitative determination method for C21 steroidal glycoside in Asclepiadaceae plants as homologous health food ,the functional group reaction method of C21 steroidal glycoside’s quantitative determination was studied in this paper after the research on their extraction method.The sulfonic mercuric acetate reagent method,which was unique to 3-hydrooxyl steroids,was used to determine the C3-OH on the aglycones directly in order to deternine the glycosides indirectly .The results showed that the method was feasible .

Key words: C21 steroidal glycosides, 3-hydrooxyl steroids , Sulfonic mercuric reagent method